Yeah... at least at PAPA / Pinburgh it is. if a ball goes in the shooter lane during play, you have to plunge it out of the lane ASAP. Even on games where having the ball go back in the shooter lane is a feature (4 Million BC). I learned this when I had to play on 4 Million BC from another player.

If you leave it in the lane, especially if you are in multiball and it doesn't auto-plunge, this is considered an unfair advantage (even though the game rules/design allows it). But tourney rules are rules, gotta follow em.

As a tournament director, I'd try to prevent a game like this from being in a lineup, if possible, given the experiences I've had and the grumbling I dealt with from fellow players. It's hard enough to play well while remembering what's going on the in the main playfield, let alone the shooter lane. If something isn't easy to control or enforce via the game rules or mechanically, I think its unfair to force the player to play around it. My opinion.