I just started using the Shotgun, and I noticed that when I was shooting rapidly and reloading, I often got booted from the server. Also it happened if I was holding the r button while shooting the shotty. This was on GH 1, which uses Pyspades, dunno if that makes a difference. This happened often enough that I went back to using the rifle for the rest of the game...
EDIT: every time this happened I was also crouching (holding ctrl)