Quote Originally Posted by Bob the Insane View Post
I have seen the issue too...

I have a suspicion that it is linked to the outcome of the Sally battle. I beleive there are multiple possible results. If you lose (as the besieger) then you are driven away. If you win you stay, but I suspect that if you have a close victory then you stay in place but the siege is broken. This then allows the auto-generated garrison to refresh back to full strength.

Just a suspicion...
This sounds plausible. Someone should do tests! (Someone with more patience than I have ).