Can't cancel Non-aggression pact

[Karolus Rex]

So I made a non-aggression pact with the SU earlier in the game, playing as Germany, so that I could finish off France, Italy, and the Balkans first somewhat safely. I can't see anywhere how long ago the pact started but the info screen in diplomacy says I need 100% of their troops on our common border stationed on the border in order to cancel the pact and that I have 92%.

The problem: I have 14 armies each 24 divisions strong stationed on our border. That comes down to 336 divisions. The SU on the other hand has around 150 - 200 divisions on our border (they're fighting Japan too). So I outnumber them somewhere between 1.7 - 2.2 times but I still can't cancel the pact.

So then I sent ALL of my garrison divisions (around 174 of them) to the border as well. AND NOW I SUDDENLY ONLY HAVE 83% of the needed troops. How does this work? I don't understand? I don't want to lose 20% stability for joining the war if I don't have to.

The only answer I can come up with is that the text means to say you need 100% of their TOTAL number of divisions (which is insanely stupid if this is the case). Or perhaps it actually looks at the number of battalions or something.