[Haskell] Perhaps a bug in GHC 6.10

Hi, One of my students wrote code like this: prop_blank s (i,j) li = if i==li then do if something then True else False else prop_blank (...) (i,j) (li+1) This code is not accepted from GHC 6.8.3 because Bool is not a monad. In particular the error message is: Sudoku.hs:269:5: Couldn't match expected type `Bool' against inferred type `a b' In the expression: ...... Surprisingly the same code is accepted from GHC 6.10. This looks like a bug for me. The easiest way to reproduce this is to try to evaluate:

do True

in GHCi with GHC 6.8.3 and with GHC 6.10 Is there any reason to accept this code? Regards, Krasimir