This is a ZOC question. I’m Venice. At war with Ottomans. My March, Serbia is in the war with me. Serbia’s owns Macedonia and Sofia. Macedonia has a fully garrisoned level 6 fort. Ottomans own Erdine, Thessaly, and Kastoria. Ottoman army marches from Erdine to Macedonia and sieges the fort. Ok. No surprise. Two days later, ottoman army departs Macedonia by marching into Thessaly. After wrecking havoc on my Army sieging Athens, the Ottomans walk back to Macedonia and pass through back to Erdine. This repeats several times during the war. Can someone explain to me the exception to the ZOC rule that allowed them to do that?