Interesting...

[Shade]

Apparently if you are reduced to just your cities, people can keep attacking you, the message is 'you held your defense and your enemy was repelled' but if they use sack, they still take your money and food. Perhaps not a bug, but still interesting.

[The Lady Shael]

Mm, I think that's expected. It'd be unfair if they sacked you and didn't get anything back, since you are still alive after all.