It IS a bug if you cancel your siege weapon & re-use the SAME key. Meaning you cancel re-use without using keys.
I can assure you none of our clan members did this, because K2 fixed that bug!!!!! If you cancel your siege weapon and re-use it, it will use a NEW key, meaning if people do this they are loosing a lot of money to heal (1.5 mill for a heal...). This is not a bug, it is same as getting a new buff from priests. It has been posted many times.