Instance Declaration discrepancy

[Saswat Anand]

class MyShow a where
 sh :: a -> String

instance (Integral a) => Show a where
 sh = "Integer " + show a

Ghc 5.00.1 (with -fglasgow-exts) does not accept the above, while hugs with
extensions has no problem with this. Is it a bug?

Thanks,
S