Confirmed that it does what you are observing in MAMEUI v176.
But it doesn't do that in my latest compile of non-UI. So either it's only in MAMEUI or it's been fixed in the main source. The next release(177) should be tomorrow & UI should follow shortly after.
I'd wait & see if that fixes it, then report back.
Hope that helps with your sanity!
Pessimist: Oh, this can't get any worse!
Optimist: Yes, it can!