Two battles for the price of one??

[LDiCesare]

vfb said:
It's the same commanders on both sides with the same names.

That doesn't mean it's not an event.
If the code goes like this:
1)Random events generate extra units.
2)Fight battles.
3)Fight battles due to random events.
4)Compute flight of surviving units.
You would see the situation you describe.