Besieged- only 1 turn left - AI is taking settlement without battle !?!

[MunichRules]

Is this normal:
I was besieged and only 1 turn is left before city surrrenders. When i click next turn ii will loose the settlement without any battle to the enemy. Was this already in Vanilla. I can not remember ever have taken any settlement just besieging till the last turn without any battle. Why can i not defend the settlement in the last turn ?

[Miraj]

Umm, if you don't sally forth before the last turn, yes you lose that settlement. Welcome to TW.