That's no bug but expected behavior because the UME variant uses the MAME history.dat formatting... only the MESS variant uses its own sysinfo.dat formatting. That's what UME brings us because there's no way to find out if a set is from MAME or MESS, that is, I decided for the formatting of the majority of sets (which are the ones from MAME, of course)... so get used to it or use the MAME/MESS variants separately, which is what I recommend to everyone.

A mind is like a parachute. It doesn't work unless it's open. [Frank Zappa]