[Olm]

I've got a game mechanics question regarding another game:

I had troops in Province A, the enemy had troops in province B.
Now I moved all my troops to B.
It seems he moved his troops to A.

I expected a clash of all troops in either A or B, depending on who is faster.

But the result was a battle in A AND B with my troops being split.

My understanding was that troops from one province move together. Is that wrong, or did something else happen, which I did not take into account?