I'm only on level 26 and have hit the same problem.
What's worse; I can't restart since "save and exit" saves the bugged game-state.
To give a little more info for you guys at popcap (who, on a side note, are awesome):
The level configuration is as follows: all of the lanes span the full screen (eg, no seagulls) except for the bottom-most lane which is four squares long.
The glitch appears to result in an invisable, 0-damaga-dealing zombie on the second to top lane which does not seem to move from the square farthest to the right (I'm thinking it might be a midget-cannon).
I have experimented with all the plants Ibrought into the level to no avail;
-kernal-pults and winter melons will all fire at this same spot if they are on that row.
-snap dragons in any of the 3 right-most squares on the suspect lane and the lanes adjacent to it will attack but no response anywhere else.
-tall-nuts take no damage regardless of how long they are left in that (or any) square.
-cherry bombs and manually-launched lawnmowers have no effect.
-spikerocks will attack if placed on the suspect square but will take no damage (such as if they were attacked by a gargantaur or rolled-over).
Is there any way to manually reset the progress I've made in this challenge (or even just reset the level, even if that means going in without plant food, or other progress markers)?
Please fix this bug. I imagine (pardon my ignorance if this is not the case) that a timer-checker in the Dead Man's Booty levels which would despawn then restart/respawn any zombies which neither move, take damage, nor take status effects over a given period of time might help. More likely, it could just be a memory leak from something like a midget cannon or midget barrel being destroyed when an effect (EG the butter from a kernal-pult or the slow of the winter melon) being applied to the object as it despawns from being destroyed by it's own properties (the cannon's self destruct or the barrel breaking on a spikerock).
