Better Handling of Duplicate Type Synonym Instances

[softmechanics]

Consider the following example:
{-# LANGUAGE TypeSynonymInstances, ContextConstraints #-}

type A = Int

class Test a where
  test :: a -> [Char]

instance Test Int where
  test _ = "Int"

instance Test A where
  test _ = "A"       

main = do print $ test (0::Int)
          print $ test (0::A)

The two instances are considered duplicates of each other. ContextConstraints allows them, but always uses the first declared instance (in this case, Test Int). Distinguish between instances for a type and instances for synonyms.