I was once shooting my SP01 in competition. When I was called to the line, I slapped in the mag and "made ready". Buzzer goes off, but the gun wouldn't fire. I cleared the weapon and it still refused to fire. The fit at the bottom of the grip was perfect. The mag latching mechanism worked perfectly. There was absolutely zero external indication of what was wrong. I locked the slide back and looked into the breach. I had inserted a mag from my P01 which was identical in every detail, except that it was 1/4" lower in the feed area. The slide had simply not been able to strip and feed a round.
My point is, there are numerous CZ mags and they all look so nearly identical that at a casual glance no one can tell them apart. That day I learned an important lesson about segregating my mags.
Simple stuff like this can get you killed.