This won't necessarily be a bug. I assume you are using analog telephone trunks here? Frequently, the only way you can determine the remote party has disconnected with analog trunks is by the tones that get played out, and unfortunately these are different in different countries. Your issue is likely that the disconnect tone is not being recognised and the fix for this is really to get a Russian country pack, and as I said in my reply to your other post, that may be a while yet.
Cheers,
Dave.
