I too had this issue. [URL]http://glocktalk.com/forums/showthread.php?t=1420934[/URL]
I have fired maybe 200 more rounds since my last post on that thread and have not had another issue. However, all those 200 rounds and the 150 before, mentioned in the post were factory loaded (Underwood and AE) or first time handloads. No once fired brass out of this last 350 rounds, all new, never fired. I am now wondering if there could be a connection.
Good luck and please keep us up to date with the issue.