overloaded strings cause core lint failure

The overloaded strings extension isn't getting past core lint in the HEAD, e.g. test tc224:

*** Core Lint Errors: in result of Desugar ***
<no location info>:
    In the expression: T.greet1 (GHC.Base.unpackCString# "hello")
    Argument value doesn't match argument type:
    Fun type: T.MyString -> T.MyString
    Arg type: [GHC.Base.Char]
    Arg: GHC.Base.unpackCString# "hello"
*** Offending Program ***
[...]

Trac metadata

Trac field	Value
Version	6.7
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler (Type checker)
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system	Unknown
Architecture	Unknown