Compiler error implies incorrect implicit import of a ((->)a) Monad instance

Take the following (incorrect) source:

fun :: Integer -> String
fun x = "123"

main = do
  s <- readFile "file.in"
  let m = read s
  writeFile "file.out" (return fun m)

Compile it:

jkff@jkff-laptop:~$ ghci tmp.hs
GHCi, version 6.10.2: http://www.haskell.org/ghc/  :? for help
Loading package ghc-prim ... linking ... done.
Loading package integer ... linking ... done.
Loading package base ... linking ... done.
[1 of 1] Compiling Main             ( tmp.hs, interpreted )

tmp.hs:8:31:
    Couldn't match expected type `String'
           against inferred type `Integer -> String'
    In the first argument of `return', namely `fun'
    In the second argument of `writeFile', namely `(return fun m)'
    In the expression: writeFile "file.out" (return fun m)
Failed, modules loaded: none.

The error looks like if the compiler has implicitly imported Control.Monad.Instances including the instance for ((->)a). It shouldn't have done so, because Prelude doesn't include this instance. NoImplicitPrelude doesn't help.

Trac metadata

Trac field	Value
Version	6.10.2
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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