Unexpected Pickup statistics with small float weights

[skyuchukov-bp]

Pickup gem version: 0.0.11
Test cases:

Sum approaching 1:
(1..10000).map { Pickup.new({"X1" => 0.11, "Y" => 0.78, "X2" => 0.11}).pick() }
Result frequency table (actual): [["X1", 10000]]
Comment: One of the elements was chosen always, and it has one of the 2 smallest weights

Sum above 1, but with a small element:
(1..10000).map { Pickup.new({"X" => 0.11, "Y" => 1.01, "Z" => 1.11}).pick() }
Result frequency table (actual): [["Y", 4925], ["X", 5075]]
Comment: No Z in the results, this might already be reported in #7

Sum above 1, each weight at least twice as big/small as the other two:
(1..10000).map { Pickup.new({"X" => 0.11, "Y" => 1.01, "Z" => 2.11}).pick() }
Result frequency table (actual): [["Z", 3323], ["X", 3333], ["Y", 3344]]
Comment: Items in the result have equal distribution, albeit input weights for X and Z having >19 times difference

P.s. Frequency tables calculated via this helper function:

def frequency_table(collection)
  table = collection.inject(Hash.new(0)) { |hash, element| hash[element] += 1; hash }
  table.sort_by { |_key, value| value }
end