I have confirmed your walls do in fact have a bug causing them to rebuild. We will have a fix for this as soon as possible. At latest it will be in the next patch. I have sent you some crown codes in your forum mail box so you can fast build another city if you so choose to until we have it fixed. Thanks for your patience. If there is anything else I can do please let me know.
If I always appear prepared, it is because before entering on an undertaking, I have meditated for long and foreseen what may occur.
--Napoleon Bonaparte, 1831