Am I missing something here?
Okay, this gets kinda complicated. I'm Muscowy, things are going ok. Annexed Yaro, bribed the GH off my back, when I got a mission to annex Ryazan. They're allied with Novgorod, but I think "Okay, I'll hit Ryazan real hard and then figure something out with Nov." So I war dec, get Ryazan on the ropes while keeping Novgorod busy, and annex Ryazan. During this, Novgorod decides to war dec Tver. Next mission? Vassalize Tver.
So now I'm coming to Tver's rescue, even though we're not allies, because I figure Novgorod will just annex them and mission failed. I manage to defeat Novgorod (it was pretty close for a while there), keeping him down while Tver is taking territory. I figure Tver will make peace soon, Nov is out of the fight, so I war dec Tver. Tver makes peace, taking three provinces, but not before most of my troops are in position to seige him.
Tver has six regiments in Novgorod province. He wants to move them to Rzhev to break my seige. But I have six regiments there too, and more nearby to call in. So he issues the move order, cancels it, re-issues, re-cancels, so on, so forth. I decide to break the loop and send some men to Novgorod. They get there, then stand around watching Tver's army going around in circles... The two armies never actually start fighting...