I also have this problem. As you described it, that means I want to build a 45 degree piece, the blueprint is okay, then confirm and the blueprint jumps to straight.
 
	Or the blueprint is okay, after confirming it, the Blueprint  jumps 2-3 degrees (floor, walls and stairs).
 
	But this only after a while. I can build 3 - 4 floors normally, then it starts.
 
	 
 
	Please fix this Obsidian.