Hello. The bug has something to do with low amount of memory, memory consuming programs and high swapping. Hang is caused by a system that is unavailable to unmount swap disk.
I think this is a severe bug since I've broken several file systems (virtual fortunately) because of the hard boot after this bug. If I add memory to buggy virtual machine, then this bug disappears, so adding memory should be a workaround. BR, -Risto