Late to your posts but...
Nice work on the sub-frame! Even better, the design is rock solid and better than just welding in pre-made sub-frame connectors sold here in the USA.
The window issue was strange and one I've never seen before, this even while twisting some rear body roff and fender panels on a drag race car (69 Camaro however). I wonder if the glass had been removed before (i.e. not OEM factory installed) and when it was re-installed, one corner or so actually touched the steel bodywork (as opposed being totally surround by the flexy rubber seal).