Annoying AI

So i was playing As Byzantium (Empire of the Romans), whilst i was preparing to conquer the rest of greece, my ally Hungary, with no sea connected provinces, attacked Morea (Greek minor) and annexed it, how can Hungary annex Morea when it has no Sea connected provinces? Screenshot: https://gyazo.com/b8dfeb7a27a4f4bb59340e9dae92a236

Please fix.