I culture bombed a nearby city state (Tyre) in order to capture its source of silver. A while later, my nearest neighbour (Siam) captured Tyre. At this point I still had access to the silver. However I went to war with Siam in order to liberate Tyre, and upon doing so, Tyre had its original borders back, meaning I lose access to the silver. Attached is the relevant saved game. Simply note the silver deposit, liberate Tyre, and note the change in border. I searched and did not find a thread for this.