Ah, great. The mailing list thread I read had people saying things more like "it is broken and there's no way to do it properly because it can sometimes cause crashes and inconsistent X server state, go away", which I thought rather peculiar because if a grab has gone wild and can't be broken the user is going to be shooting down the whole X server soon, inconsistent state or no.
But if it *is* possible to do it properly and it's coming back, excellent!