I might as well tell the whole story:
My FiL liked the pistol so much that I gave it to him as a Christmas gift. He had plenty of 40 caliber brass, so he bought some dies and loaded some up. He is a careful guy and researched several websites before he loaded up a few trial batches. He made some mild, medium, and spicy loads.
He shot a bunch of mild and medium loads with no problems. Then he shot a few of the hotter ones and noticed that the cases were bulging a bit. If either one of us had been thinking AT ALL just then, that would have been the end of it. But no, he tried a few more rounds and noticed that his frame suddenly had a crack in it.
Apparently I was intent on out-idioting him. He showed me what had happened and asked if I would try a few rounds in my Beretta 96. I am not usually that stupid, but I said "Sure!" and loaded a few rounds in the magazine. I was surprised, but shouldn't have been, when it disassembled itself on the third round.
When we got back to his house we got the Beretta re-assembled and it has been fine ever since. He illogically insisted that the CZ-P09 was at fault, rather than the ammo. He sent it in under warranty and they wouldn't replace it. (I don't blame them.)
If you look at it, it cracked where some polymer had been removed to make room for metal rail inserts. It's easy to see that that's the weakest part of the frame. Luckily for me, my Beretta is a bit sturdier.