Retreating Army

[Mano3]

During my last game, Justinian declared war on me and ALL of my troops in my city bordering Byzantine 'retreated' to one of my cities on the opposite side of my little country! My size 10 city was completely abandoned and Justinian just marched on in and captured it. I'm praying this is just a bug...

PS: I re-played the offending turns and it did not happen again when Justinian declared war on me...