Dracula mission 2 - return of the dragon glitch?

Before I made it to Imperial, I was no longer in control of my units - they had switched to neutral and suddenly I was playing as Hungary - green.

How does this even happen?

Seems like the scenario is about defending 'Bran castle' and keeping Dracula alive - not even playing as Dracula makes no sense.

There was no prompt or speech.

Did I hit some hotkey that switches team control?

Very confused