Simon Peyton Jones via ghc-devs writes:

Ben I've just pushed a fix to Trac #13804. It may belong on the 8.2 branch too because it fixes a regression wrt 8.0. I can't test on my Unix box, because I'm away from it for a few days, but I've validated on windows. Can you just check it's ok, and fix up or revert if not?

Of course. Cheers, - Ben