Apologies if this is a known bug with SCW or M&B, I have trawled the forums without seeing any mention of it.
I come back to Zendar to find a massive peasant rebellion on its doorstep, 1000 troops or so. So I grind through them, good fun, and rescue some cool prisoners at the end.
Afterwards I notice a strange looking enemy with 0 + 200. I go to battle, and it informs me I have 1 troop and the enemy has zero. I ride around for 10 seconds on the battle map and it declares I've won. I get the loot and prisoners, but my original army is gone. Marnid too. The only members of my army are now the prisoners I just rescued.
Cheers for the fun mod though Mirathei.