This is probably a silly question, but are any of the people having trouble with their GLOCKs left eye dominant? My GLOCK (gen 4 23) just pops brass out over my right shoulder, but I bet if I moved it over a few inches to shoot with my left eye, it might hit my face sometimes.
I actually am left eye dominant and I know for fact that it is a factor for me with certain guns. However, I recently owned a Glock 23 that kicked cases well away from me, unlike the Glock 19 I had. I think it's much more a problem with the 9mm Glocks than the others.