pthread mutex error building 6.10 on NetBSD

I tried to build GHC 6.10.1 on NetBSD 4.0 this afternoon, and ran into an error, where cabal-bin calls the stage2 ghc in utils/installPackage. pthread_mutex_unlock() is called, evidently from fileLock(), with an invalid mutex. NetBSD's pthread implementation differs from Linux in its intolerance of such things. I have found errors where someone forgets that a mutex was never used and tries to unlock it. I guess you could do that all day long on Linux without noticing anything, but NetBSD aborts the program. In the present case, I don't see anything like that wrong in rts/FileLock.c, though. I'm stumped. So I'm checking, has anyone else built 6.10 on NetBSD? Donn