Actually, scratch that altogether. What I think happened was the old 'the thing I was winding up an attack for died so I'm just going to launch this projectile at a 45ish degree angle' bug. I just happened to boost the tower at the same instant to add a new wrinkle.
Still suspect that when the target dies in the frame or two winding up to a projectile attack, the projectile tries to use the location data of the dead critter which got wiped to one degree or another.
But that's my suspicion and it's still on the not gonna get fixed list if I remember right.
Nifty setup on the new forums at any rate.