ghci misinterprets "early" unicode characters

It seems as if ghci misinterprets unicode characters if they occur too early in a source file.

$ cat test.hs
--data A = A -- example will not work if this line is commented
笑 :: [a] -> Int
笑 = length

$ ghci test.hs
GHCi, version 6.10.4: 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             ( test.hs, interpreted )

test.hs:2:0:
    Illegal signature in pattern: [a] -> Int 笑
        Use -XScopedTypeVariables to permit it
Failed, modules loaded: none.
Prelude>

Uncommenting the first line makes the problem go away.

Trac metadata

Trac field	Value
Version	6.10.4
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	GHCi
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