These veterans speak truth.
I think I learned the word "fumbleduck" and some other creative nouns and adjectives when that first happened to me. Fortunately, prior experience with zero-backlash gearing in encoders for servo systems provided me with some basis for reassembling the thing. Unfortunately, I still got to broaden my vocabulary to the level of making half the Royal Navy turn pink.
These seem to commonly work their way loose, and with no case cover in place, could potentially just walk out the end of the frame. I'm not sure if the pinion dears were ever staked to the end of the shaft, but after 40 years it seems that none of them are any more. That can lead you to your own semantic expansion into the realm of "corkslapper" and an occasional "dog game feather-mucker" among others. It's only a frustration, since it CAN be put back together after the initial exasperation of watching it dismantle itself.
We feel your pain. I've considered LocTite 262 or bearing retainer to help this, but haven't tried it yet. I really don't want to, since I already have enough words to keep organized.