[Turin]

I guess this happened:
First the game checks the movement between him and your pretender army.
His army wins and wants to move to your pretender´s province, your pretender armyies´ orders get overwritten to defend, because the battle should take place in the province held by your pretender´s army.

Then the game checks the movement between your secondary army and his main army. Your army wins, his armies´ movement orders get overwritten to defend and we get the turnfile you got.

Note that your scout made it through with his sneaking orders, which would fit with my guess.