I'm having a lot of problems with the game selecting the wrong level of multi-level areas since I picked up this playthrough after a month or two off. It's a major pain and I don't know what's different that is causing it. I seem to have a bit more lag, as well, but that might just be my memory playing tricks on me. Either way, I try to click where I want my characters to go, and it'll frequently target something on the wrong level (usually under) and the characters will scramble around trying to find a path, usually running in the opposite direction of where I'm trying to go, and disappearing off my screen before I can figure out where they went to.
Are you by any chance an Old Age Person like me? My son keeps on grumbling that I'm playing almost exclusively with the mouse, instead of having my fingers dance over the WASD keys ...