I have a suspicion - but it's just a suspicion - that your extractor is too tight; and it's slamming the spent casings downward and into the ejection port lip as they come out of the pistol.
If I'm correct, this problem will become less and less the more the pistol is fired. My immediate suggestion would be to place a few drops of oil on the extractor claw prior to using the pistol.
If the problem's still there after 200-250 rounds, you'll have to start looking for another solution. In the meantime, let Glock Tech Support know. Send them a letter and a few spent cases. See what they say.
Here's a G-33 schematic for you to reference:
http://www.gunpartscorp.com/catalog/Products.aspx?catid=2302 The extractor is part #11. The ejector is the rod on the front of part #23 (The trigger housing unit.)