ST monad bug

hi i run into a bug in the implementation if the ST monad: f = fixST $ const $ return 'z' >>= return Main> runST f '\ Program error: Prelude.!!: negative index it looks like there is a bug with the pointers and the wrong type of thing gets written somewhere. here is another example: f = fixST $ const $ return 'z' >>= return . ord Main> runST f ('z',) bye iavor