Interesting. Kevin and I were video taped with a high speed camera, and one thing I noticed was with identical guns, identical ammo (from the same case) and the same shooting stance and style, Kevin's brass went straight up and landed on the brim of his hat. Mine went to my right landing about 2ft away. I'm guessing just minor differences in extractor spring and in the ejector can cause a radical change in trajectory.
I'm betting any qualified Glock armorer could make a quick adjustment. A search on the Glock forum might bring up some remedies.