fromDynamic crashes ghci

Loading the following code into ghci and evaluating x
causes a segmentation fault:

data Foo a = Foo a

instance Typeable (Foo a) where
  typeOf x = mkAppTy (mkTyCon "BAD") []

x :: Maybe (Foo Char)
x = fromDynamic (toDyn (Foo "abc"))

This is not a problem for ghc.

The version of ghci is 5.00.2

I'm running on linux, not sure what vintage I'm afraid.

By the way, the reason I wrote this code was because I
was trying to figure out what role the type string
plays in the Dynamic library.  The documentation seems
to indicate that it is checked for equality every time
fromDyn or fromDynamic is called, but that doesn't seem
to be the case.  More documentation on what the string
does, and how to construct it correctly, would be
appreciated.  I was trying to figure out if I could
make this type Typeable:

data Name a = String

Trac metadata

Trac field	Value
Version	None
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	ResolvedFixed
Component	None
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