A bug in hugs

Hugs version: Dec 2001. Platform: Windows. Both WinHugs and command line hugs have the same bug. start hugs with -98 option and try the following program: class Monad m => ExMonad where raise :: String-> m a instead of reporting an error, an internal error is raised: INTERNAL ERROR: inheritFundeps - predicate failed to match it's own head! Regards. Deling