Breaking alliances

I finished a Tamurkhan long campaign yesterday. The final objective required was to conquer Nuln. By the time I got to the old world, all big order factions were in defensice alliances, so theoretically, once I declared war on Nuln I was supposed to fight everyone and their grandma. Kislev, Karl Franz, Thorgrim etc. So just out of curiosity I tried asking them to break their defensive alliances, just to see how expensive that would be. To my surprise, the option was completely balanced for most factions. I only had to ask and they did it, no money asked.

So in a single turn all major factions in the area broke their defensive alliances without asking for a penny. Is this normal behavior that somehow escaped me after hundreds of hours of gameplay? Or some unintended consequence of latest patches?

I was playing on L/VH and not all alliances were free to break, but most of them were, mainly those between empire and kislev factions.