Express down window question
 

I have done a search but can't seem to find any help on a strange express down window problem.
Car is a 91 300D. The express down windows on the drivers side only goes down about half way then stops. Manually lowering the window the rest of the way works fine. I tried helping the window down by pushing but that made it worse. Then it only went down about 1/3 of the way. I do electrical work on cars for a living and I know I should know what the problem is, but this one defies logic. Express down usually works by measuring the current and when it detects a large jump in current it switches the window off.
Mercedes must do it differently.
This is the strange thing I found out while trying to diagnose this problem;
If I start the windows going down then try to hold it up which would make most systems stop, this one continues down until I loose my grip on the window. It stops at that point, but it will be allmost all the way down.
Anyone have any ideas on this one?
Thanks
PS. My wife will very much appriciate the problem being resolved.

Bump
Has anyone had any experience with this problem?