This has happened on 2 occasions.

My Hayasdan army beseiging Charax is attacked from behind by a small Seleucid army consisting of a unit of Hellenic Bodyguards, and 1 unit of Hellenic archers. The besieged Seleucid army of Charax (which consists of 1 unit of Hellenic archers, 2 units of Native Hellenic Spearmen, and 1 unit of heavy spearmen) are used as reinforcements.

Anyway, I win a ridiculously easy clear victory. I then choose to occupy Charax, and then boom, the game gives me an all too convenient CTD.

Here is the link to my save game: http://uploaded.to/?id=tsmcy5