The Dude meter doesn't reset until the game is jackpotted during Super Dude. The Dude meter will continue to build one increment for every multiball and your Dude level carries over from game to game. Then, once you multiball in Super Dude and collect the jackpot, the Dude meter will reset back to Plain Dude.
I thought this was wrong on mine too originally, but now I think it makes the game more fun. Your best scoring games will *usually* happen during Super Dude games since the jackpot is bigger, so it's something to work toward. Blackbeard might be right about tournament mode, but really no reason to zero out the Dude meter as you always want to working toward Super Dude.