Wireshark performance - freezing when stopping capture / closing file

I'm capturing several remote interfaces with rpcap://host/emac0 and saving to files with size 50MB each. After a couple of hours when I try to stop the captures many of them are freezing. With each "stop capture" a new window pops up "Closing file" that will stay on screen forever. The parent window stays freezing so I cannot close it (only to kill in taskman). Number of "Closing file" windows are actully more then the number of started captures. For 10 captures I got 30 "closing file"-s.

Anybody experienced the same ? Solution ? Thanks