Thank you for the information, this will help a lot, too.
Had the same issue for a while now (since 1.42 was beta). The .tmp.sav files are only 1kb, but they are located in the same folder as the older versions ( This PC > Documents > Mount and Blade II Bannerlord > Game Saves > Native)
And dear Taleworld, you really need to fix this guys. It seems to be happening to more and more people with each update. Not being able to save your game is pretty much second only to not being able to launch or install your game when it comes to deal-breakers. Just my humble opinion.
Keep up your great work, and I'll go back to 1.41 for now...