My understanding of MAMETesters at
00501: liberatr: Select any wave above 16 (19 or 22) and the game resets on the planet screen. - MAME Testerssuggests that this emulation issue was fixed in MAME v 0.146
Retro Uprising probably supports an earlier version of MAME (v 0.106?) so you could either play the game outside RU using a newer version of MAME, or wait to see if RU changes to a newer MAME.