Sig P250 ultra compact in S&W 40

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I picked up a Sig P250 ultra Compact in 40 last week. I wanted to get another 40 caliber carry gun as a companion to my Walther PPS. I've owned a P226 and sold it, but kept my P220. I took the P250 to the range Friday and put 100rds through it without any issues. Nice shooting DOA pistol. Trigger is fine, but the reset is longer than I'm used to on my Glocks. I shot it in our club IDPA match had no issues with function at all. I had my wife shoot it today with an extended 13rd Sig P250 magazine and had an interesting issue. While she was shooting it the slide went all the way back and stuck open. The slide stop was not engaged, but the slide was definitely stuck back. I tapped it the heel of my hand and it went back into battery no problem. Happened to my wife 3 times and has not happened to me at all. I tried to reproduce the problem, but could not. I think she might have been squeezing the magazine as the 13rd sticks out of the ultra compact frame. I think the mag might have been tweaked in the frame a bit and could have caused the slide to lock back without the slide stop engaged. Has anyone else experienced this with a P250? Again it only happened to my wife and not me. Strange...Otherwise I really like the gun and want to carry it as well. Overall I'm very impressed with this pistol.