I don't mean to sound like a jerk, but are you sure the brass is not first hitting a range stall or wall or something then bouncing and hitting him in the head?
I have heard of this problem with the first batch of gen4 guns. Glock worked the issue out, but it is possible they put the gun together with a bad part or an old part that got mixed in with the fresh correct parts.
It would have to be an extractor or ejector problem, it is very unusual for a gun to throw brass straight back, and I am thinking it would be an extractor problem, as the slide coming back causes the brass (held by extractor) to hit the ejector (mounted to frame), the ejector only causes the brass to be kicked out, the contact point is the extractor claw, and the ejector hits the case on the opposite side of the brass causing the brass case to be kicked out in the way designed.
Something has to be really funky in order for it to be spitting brass straight back