[Psycho]

Forts are not immediately repaired when the siege is lifted. It is just shown like that, but actually the damage still exists.

The easiest way to try - siege an empty fortress. Then move away next turn. Then return on the third turn. The damage on the third turn will be the sum of damages on the first and third turn. But during the second turn it is shown as if there is no damage. The display during the second turn while the siege is lifted is misleading.