I have had a very long running custom game going trying to see how far I can get (currently at wave 9358) and I have noticed a number of things (other than the GP value moving to 1 when you earn enough GP reported in another bug). I'm not quite sure when it started happening as I have most all animations turned off due to lag but several towers seemed to have stopped working altogether. Flamethrower, blast, splash, and freeze no longer appear to do anything. When I have it show targeting, the FT clearly targets things but never actually shoots out flame as can be seen when turning on animations. Additionally, I built a new splash, flamethrower, and blast tower and they have 0 mdps.

Also, it appears that at some point firestorm stops doing any sort of noticeable damage. I am guessing that it probably caps out with the integer limit as well. This doesn't seem to affect Nuke, ball lightning, LOIC, or smoke.