I wouldn't call it common.
I've run a lot of rounds through my CS9 & CS45 over the years. I've shot them enough to have replaced the recoil springs in each of them, and some mag springs and some of the CS45 followers, but haven't yet had to replace the mag catch nut on either of them.
I know other folks who have been running 457/908/CS45/CS9's over the years, too, and I've not yet had to replace one of the nylon mag catch nuts in their guns (or know of one popping off). I keep a couple spare plastic nuts, springs & steel mag catch bodies in my parts, though, just in case.
Armorers are told that in order to remove the plastic nuts (if service is needed that requires removal of the mag catch), a pin punch might be needed to punch out the shaft of the mag catch body from the nut. (There has to be room on the other side of the frame for the mag catch body to move, of course.) I've been told by someone at the factory that some folks have had to use needle nose pliers to pull the plastic nuts free of the mag catch bodies.
This all leads me to suspect that more often than not, they're usually snapped onto the shafts rather firmly.
Snapping the new nut onto the shaft is pretty straight forward, but the opposite end of the mag catch body (right side of frame) has to be firmly supported, not just held by the grips. This is usually done with the grips removed and frame laying on its right side, on a flat firm surface. This is a 1-time installation, so you want to get it right the first time (a new nut each time one is removed).
There have been times when I've needed to adjust the regular 3rd gen mag catch nuts & plungers, and to save the time needed to remove the grips I've just slipped a nickel under the right end of the mag catch (in front of the grip's edge) to support the end of the mag catch body, as the frame is laying on its right side on a bench. I might try that with a Value Line (American Heritage) or CS gun if I were just going to snap a new nut onto the shaft (or else just remove the grips and not be lazy and try to save a couple steps). Naturally, if I suspected a problem with the mag catch I'd remove the grips and the mag catch itself.
If the new nut came off at some point? I'd replace the mag catch body and the nut the next time. I've come across a few of the steel mag catch bodies that just didn't seem to fit or work in a particular frame/gun. Oddly enough, although I've not had to replace one of the plastic nuts in a VL/CS gun, I've had to replace an occasional steel mag catch assembly in various early 3rd gen's, and even in a few current TSW's. Go figure.
457 mag release button popoff
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