Sticky Harness

I have an on-going problem with my 7th harness. Sometimes, after I take my foot off of the treadle, it sticks in place instead of falling down with the rest of its buddies. It seems to happen more often the further into a weaving session I am. It won't stick when I first sit down at the loom, but after a few minutes it will. This has been happening for a long time, but I always thought that it had something to do with the floor being uneven at my old house. But now I'm in a new location on nice solid wood floors, and it is still happening. I have loosened bolts that might be forcing the harnesses to rub against one anther, I have oiled all the little metal hinges, I have even removed all of the harnesses and changed their order. But still, it sticks! And it really slows me down, because I need to stop and lower it with my hands.
My theory is that is might be caused by weight distribution, the unused headles tend to slide around on the harness, and maybe when there are more headles on one side than the other, the harness frame leans and gets wedged against the castle walls. But then, why doesn't it happen to the other harnesses that have just as many unused headles?

Any ideas/ suggestions? Has anyone else had this problem with the Schacht Wolf looms?