Sometimes you may come across a bug in Yabause, whether it be emulation related, UI related or whatever. It's always important to report bugs so they get fixed. But what's really important is not only that you found the bug, but all the things surrounding it.
So what to do?
In order to figure this out, you first have to keep track of which version of the software you're using, which OS you're running, etc. This may be vitally important to why the bug has appeared. Next keep track of everything you've done during that session, or better yet try to see if you can reproduce the bug. Is this a new bug? Was this working in an older version? When did it stop working? Find that out too. Once you've done that you have a few options. You can either Submit a bug report or you can discuss it on the forums.