No, it's not your imagination. Last night I finally witnessed a bizarre phenomenon previously reported by a couple of players: tanks falling from the sky on the bf1942/Tobruk map.

Next time you're playing bf1942/Tobruk on TPU, watch the skies. Eventually, you may see one or more tanks appear way up in the sky and fall to the ground. The falling tanks often contain bots. Usually these tanks are destroyed when they hit the ground, but sometimes they survive, and rejoin the fight.

So far I've been unable to determine a specific set of circumstances in which this occurs.

My assumption at this point is that there's a bug in the map source for Tobruk, possibly introduced along with the vehicle spawning changes made for TPU. Either that, or there are simply too many units on the map now.