As reported to Xoom some time ago, the important overrun tool, which allows a HC to withdraw the garrison from an attacked city, doesn’t work.
What happens is that the city enters overrun mode, and the HC isn’t given the option to withdraw it or keep it at all costs.
I tried twice in the last few months, and both times it didn’t work but I want to point out that it happened only in cities without brigades.
So I’m opening a ticket and hoping this can be resolved.