diff --git a/src/services/salesforce/bulk-api.ts b/src/services/salesforce/bulk-api.ts
index 7d915bc..946dcf8 100644
--- a/src/services/salesforce/bulk-api.ts
+++ b/src/services/salesforce/bulk-api.ts
@@ -244,6 +244,7 @@ export class BulkApiService {
       header: true,
       delimiter: ',',
       skipEmptyLines: true,
+      dynamicTyping: true,
       transformHeader: header => header.trim(),
     });
     if (parsed.errors.length > 0) {
diff --git a/src/services/salesforce/queryAll.ts b/src/services/salesforce/queryAll.ts
index 3eb708c..430a1cd 100644
--- a/src/services/salesforce/queryAll.ts
+++ b/src/services/salesforce/queryAll.ts
@@ -50,18 +50,28 @@ export async function queryAllRecords(
 }
 
 /**
- * Derives the set of column names present across the first `sampleSize` records,
- * excluding Salesforce's `attributes` envelope. Stable order of first appearance.
+ * Derives the set of column names present across all loaded records,
+ * excluding Salesforce's `attributes` envelope at any nesting level.
+ * Stable order of first appearance.
  */
-export function deriveColumns(records: Record<string, unknown>[], sampleSize = 50): string[] {
+export function deriveColumns(records: Record<string, unknown>[]): string[] {
   const cols: string[] = [];
   const seen = new Set<string>();
-  for (const record of records.slice(0, sampleSize)) {
-    for (const key of Object.keys(record)) {
-      if (key === 'attributes' || seen.has(key)) continue;
-      seen.add(key);
-      cols.push(key);
-    }
+  for (const record of records) {
+    collectKeys(record, '', seen, cols);
   }
   return cols;
 }
+
+function collectKeys(value: unknown, prefix: string, seen: Set<string>, cols: string[]): void {
+  if (value === null || value === undefined || typeof value !== 'object' || Array.isArray(value)) return;
+  for (const [k, v] of Object.entries(value as Record<string, unknown>)) {
+    if (k === 'attributes') continue;
+    const fullKey = prefix ? `${prefix}.${k}` : k;
+    if (!seen.has(fullKey)) {
+      seen.add(fullKey);
+      cols.push(fullKey);
+    }
+    collectKeys(v, fullKey, seen, cols);
+  }
+}
diff --git a/src/ui/components/ExportModal.tsx b/src/ui/components/ExportModal.tsx
index 0eee046..c11e1b0 100644
--- a/src/ui/components/ExportModal.tsx
+++ b/src/ui/components/ExportModal.tsx
@@ -15,6 +15,7 @@ export interface ExportModalProps {
   open: boolean;
   records: Record<string, unknown>[];
   columns: string[];
+  selectedColumns?: string[];
   defaultFilename?: string;
   preferences?: ExportPreferences;
   onPreferencesChange?: (preferences: ExportPreferences) => void;
@@ -34,16 +35,18 @@ export function ExportModal(props: ExportModalProps): VNode | null {
   const [filename, setFilename] = useState<string>(defaultFilename);
   const [sheetName, setSheetName] = useState<string>(props.preferences?.sheetName ?? 'Sheet1');
   const [includeMetadata, setIncludeMetadata] = useState<boolean>(props.preferences?.includeMetadata ?? false);
-  const [selectedColumns, setSelectedColumns] = useState<Set<string>>(new Set(columns));
+  const [selectedColumns, setSelectedColumns] = useState<Set<string>>(new Set(props.selectedColumns ?? columns));
   const [showColumnPicker, setShowColumnPicker] = useState<boolean>(false);
+  const [error, setError] = useState<string | null>(null);
 
   useEffect(() => {
     if (!open) return;
-    setSelectedColumns(new Set(columns));
+    setSelectedColumns(new Set(props.selectedColumns ?? columns));
     setFormat(props.preferences?.format ?? 'csv');
     setSheetName(props.preferences?.sheetName ?? 'Sheet1');
     setIncludeMetadata(props.preferences?.includeMetadata ?? false);
-  }, [open, columns, props.preferences?.format, props.preferences?.sheetName, props.preferences?.includeMetadata]);
+    setError(null);
+  }, [open, columns, props.selectedColumns, props.preferences?.format, props.preferences?.sheetName, props.preferences?.includeMetadata]);
 
   function updatePreferences(next: Partial<ExportPreferences>): void {
     props.onPreferencesChange?.({ format, sheetName, includeMetadata, ...next });
@@ -52,17 +55,39 @@ export function ExportModal(props: ExportModalProps): VNode | null {
   if (!open) return null;
 
   const handleExport = async () => {
+    setError(null);
+
+    // Validate Excel sheet name: max 31 chars, no : \ / ? * [ ]
+    if (format === 'excel') {
+      const invalidChars = /[:\\/?*\[\]]/;
+      if (!sheetName.trim()) {
+        setError('Sheet name cannot be empty.');
+        return;
+      }
+      if (sheetName.length > 31) {
+        setError('Sheet name must be 31 characters or fewer.');
+        return;
+      }
+      if (invalidChars.test(sheetName)) {
+        setError('Sheet name cannot contain : \\ / ? * [ ]');
+        return;
+      }
+    }
+
     const finalFilename = ensureCorrectExtension(filename, format);
     const columnsToExport = Array.from(selectedColumns);
 
-    await exportRecords(records, columnsToExport, {
-      format,
-      filename: finalFilename,
-      sheetName: format === 'excel' ? sheetName : undefined,
-      includeMetadata: format === 'json' ? includeMetadata : undefined,
-    });
-
-    onClose();
+    try {
+      await exportRecords(records, columnsToExport, {
+        format,
+        filename: finalFilename,
+        sheetName: format === 'excel' ? sheetName : undefined,
+        includeMetadata: format === 'json' ? includeMetadata : undefined,
+      });
+      onClose();
+    } catch (err) {
+      setError(err instanceof Error ? err.message : String(err));
+    }
   };
 
   const toggleColumn = (column: string) => {
@@ -217,6 +242,12 @@ export function ExportModal(props: ExportModalProps): VNode | null {
             )}
           </div>
 
+          {error ? (
+            <div role="alert" style="color:#b91c1c;background:#fef2f2;border:1px solid #fecaca;border-radius:8px;padding:8px 12px;font-size:13px">
+              {error}
+            </div>
+          ) : null}
+
           <div style="display:flex;gap:8px;justify-content:flex-end;padding-top:8px;border-top:1px solid var(--wl-line-2)">
             <button class="wl-btn" onClick={onClose}>Cancel</button>
             <button
diff --git a/src/ui/screens/ExportScreen.tsx b/src/ui/screens/ExportScreen.tsx
index 35f773e..9427261 100644
--- a/src/ui/screens/ExportScreen.tsx
+++ b/src/ui/screens/ExportScreen.tsx
@@ -59,9 +59,13 @@ export function ExportScreen(props: {
   const [tabNameDraft, setTabNameDraft] = useState('');
   const [workspaceLoaded, setWorkspaceLoaded] = useState(false);
   const workspaceKey = `exportWorkspace:${context?.orgId ?? 'local'}`;
+  // Track which workspaceKey the current tabs belong to, so the save effect
+  // never writes stale tabs under a new org's key during the async load gap.
+  const loadedForKeyRef = useRef<string | null>(null);
 
   useEffect(() => {
     setWorkspaceLoaded(false);
+    loadedForKeyRef.current = null;
     chrome.storage.local.get([workspaceKey], result => {
       const saved = result[workspaceKey] as { tabs?: QueryWorkspaceTab[]; activeTabId?: string } | undefined;
       if (saved?.tabs?.length) {
@@ -71,13 +75,22 @@ export function ExportScreen(props: {
         setActiveTabId(nextActive);
         onSoqlChange(restoredTabs.find(tab => tab.id === nextActive)?.soql ?? soql);
         nextTabNumber.current = restoredTabs.length + 1;
+      } else {
+        // New org with no saved workspace — reset to defaults so stale tabs
+        // from the previous org are not displayed or persisted.
+        setTabs([normalizeTab({ id: 'query-1', name: 'Query 1', soql })]);
+        setActiveTabId('query-1');
+        onSoqlChange(soql);
+        nextTabNumber.current = 2;
       }
+      loadedForKeyRef.current = workspaceKey;
       setWorkspaceLoaded(true);
     });
   }, [workspaceKey]);
 
   useEffect(() => {
     if (!workspaceLoaded) return;
+    if (loadedForKeyRef.current !== workspaceKey) return;
     chrome.storage.local.set({ [workspaceKey]: { tabs, activeTabId } });
   }, [workspaceLoaded, workspaceKey, tabs, activeTabId]);
 
diff --git a/src/ui/screens/QueryScreen.tsx b/src/ui/screens/QueryScreen.tsx
index 0077efd..1538123 100644
--- a/src/ui/screens/QueryScreen.tsx
+++ b/src/ui/screens/QueryScreen.tsx
@@ -697,7 +697,8 @@ export function QueryScreen(props: {
       <ExportModal
         open={exportOpen}
         records={flatRecords}
-        columns={selectedColumns.length ? selectedColumns : columns}
+        columns={columns}
+        selectedColumns={selectedColumns.length ? selectedColumns : columns}
         defaultFilename={`wavelink-query-${Date.now()}`}
         preferences={props.exportPreferences}
         onPreferencesChange={props.onExportPreferencesChange}
diff --git a/src/ui/utils/download.ts b/src/ui/utils/download.ts
index 8a57c40..0b77a13 100644
--- a/src/ui/utils/download.ts
+++ b/src/ui/utils/download.ts
@@ -13,7 +13,9 @@ export function downloadTextFile(filename: string, content: string, contentType:
 
 /** Build a download from bounded generated chunks instead of one giant string. */
 export function downloadBlobParts(filename: string, parts: BlobPart[], contentType: string): void {
-  const blob = new Blob(parts, { type: contentType });
+  // Prepend UTF-8 BOM for CSV so Windows Excel opens it correctly (issue #72)
+  const finalParts: BlobPart[] = contentType === 'text/csv' ? ['', ...parts] : parts;
+  const blob = new Blob(finalParts, { type: contentType });
   const url = URL.createObjectURL(blob);
   const a = document.createElement('a');
   a.href = url;
diff --git a/src/ui/utils/records.ts b/src/ui/utils/records.ts
index 326bcaf..357ce76 100644
--- a/src/ui/utils/records.ts
+++ b/src/ui/utils/records.ts
@@ -24,7 +24,6 @@ export function flattenRecord(
   const out: FlatRecord = {};
 
   function visit(value: unknown, path: string, depth: number): void {
-    if (path === 'attributes') return;
     if (value === undefined) return;
 
     if (value === null) {
@@ -48,6 +47,7 @@ export function flattenRecord(
         return;
       }
       for (const [k, v] of Object.entries(value)) {
+        if (k === 'attributes') continue;
         const nextPath = path ? `${path}.${k}` : k;
         visit(v, nextPath, depth + 1);
       }
@@ -66,9 +66,9 @@ export function flattenRecord(
   return cleaned;
 }
 
-export function deriveColumns(records: Array<Record<string, unknown>>, limit: number = 50): string[] {
+export function deriveColumns(records: Array<Record<string, unknown>>): string[] {
   const cols = new Set<string>();
-  for (const rec of records.slice(0, limit)) {
+  for (const rec of records) {
     const flat = flattenRecord(rec);
     for (const key of Object.keys(flat)) {
       cols.add(key);
diff --git a/tests/unit/queryAll.test.ts b/tests/unit/queryAll.test.ts
index f85c4d2..571ad05 100644
--- a/tests/unit/queryAll.test.ts
+++ b/tests/unit/queryAll.test.ts
@@ -75,11 +75,11 @@ describe('deriveColumns', () => {
     expect(deriveColumns(records)).toEqual(['Id', 'Name', 'Industry']);
   });
 
-  it('only samples up to sampleSize records', () => {
+  it('derives columns from all records, not just a sample', () => {
     const records = [
       { Id: '1' },
-      { Id: '2', Late: 'x' }, // beyond sampleSize=1, so Late not picked up
+      { Id: '2', Late: 'x' },
     ];
-    expect(deriveColumns(records, 1)).toEqual(['Id']);
+    expect(deriveColumns(records)).toEqual(['Id', 'Late']);
   });
 });