This is no fluke but rather a known issue of the past. It’s been a while since got these links/files, my memory is fuzzy. The affected serial number starts with an E and I think later versions have shorter rails. Glock has replaced the frames at no cost but you may have to pay shipping one way and have the cost/issue of having to re-DROS.
http://www.texaschlforum.com/viewtopic.php?f=23&t=42040
http://TheFiringLine.com/forums/showthread.php?t=134665