Not a feature, not a flaw, just a random event when angles and inertia line up. The old and very well used Canadian Inglis versions of Browning hi-powers, that I first trained with, almost all did it almost always. So we got used to it. Palm hits mag with fingers pointing up, if slide goes forward then great carry on with next, if not fingers continue over top, cup the slide, slingshot, carry on. That way you can shave time when it happens, but are not stalled to think if it does not. Has happened on my BHP almost always since I bought it used. Started on my Xd9 around 3000 rounds. Just recently started on my SR1911 somewhere north of 4000.
Eta, some advise: don't try to modify slide holdback so it happens more. Could just mess up the slide lock. Hard to make random mechanical coincidence into normal.
A proud Canadian, respectfully residing in the United States of America, and happily living in Arizona
Royal Canadian Air Force 82-94, Canadian Reserve Army 80-82
NRA Member, Certified Instructor Shotgun, Certified Range Safety Officer
other forums I like: rugerforum.net canadiangunnutz.com
XD9 service and XDs45, a few others around here someplace (wink) Still lovin' my SR1911