Well, I seem to be getting all the good luck lately (haha).
Started a Seleucid Empire campaign; only two mods installed through the Steam Workshop (Dresden's '2TPY' mod and Hellbent's 'TTT' mod). Everything's going well at first; invaded and captured Salamis using my larger of 2 starting armies. Then as I moved it towards Jerusalem in order to march on Egypt, I noticed this:
So, initially, I thought "

yeah! Free army!", but when I tried to move the duplicate army on my territory, a "you don't have permission to access this territory screen" popped up, with only "Declare War" and "Cancel Order" available. So I clicked declare war, even though it was my own territory. Then I got this:
So, I managed to declare war on myself, my remaining satraps declared war on me too, and worst of all, my duplicate army disappeared.
Woe is me.