Comment 84 for bug 194214

If I'm not mistaken (which isn't all that unlikely, this stuff is complex), there is a problem with the workaround:
If the sequence is Freeze - UNWRAP - Thaw - COND_WRAP (if that's possible?), then after thawing we'll have dev->public.processInputProc == dev->public.realInputProc, so the assignment device->public.processInputProc = proc in COND_WRAP goes through, allowing EnqueueEvent to escape. It's just not as bad since we haven't replaced realInputProc with EnqueueEvent.

If you're still having issues with the workaround in place, the patch attached to bug #14449 might be worth a try. In basically tries to enforce the invariant (in case of Freezing/Thawing, there might be other users of the mechanism) that
processInputProc == (!frozen ? realInputProc : EnqueueEvent).