There are a few Ops bugs like this that rear their heads very occasionally. Most frequent is what came to be known as the wave 8 bug, in which the counter for AI enemies totals one more than the number that are spawned. Would this by any chance have occurred on wave 8?
I remember that a long time ago an ex-popcap employee sheepishly admitted to this being his fault. If the map has a way for players to kill themselves, like jumping in the water at Boney Island, I think you can fix the bug by doing so. Otherwise, you're up the creek. I'm not sure if this works with AI teammates, I think the entire team must do so.
