All Cobalt RaQs have issues with the UBB. They are not a recommended platform due to very poor I/O speed. I/O speed is the major UBB bottleneck. Slow I/O + many requests -> a heavily loaded server -> slower I/O -> more requests due to speed -> more load -> slower I/O -> etc, etc...
The instant that things start to get out of synch due to delayed I/O, PNTF throws a fit and the deadlock as mentioned above occurs.