Thanks for the info! I read the item description for the 1958 Campagnolo crankset that was recently on eBay and the seller wrote that the pedal caps for those cranksets were removed within the next year or so owing to the insertion of pedals with longer threaded end sections (which obviously would cause the cap to pop out).
I would think that a pedal with a short threaded end section and too much grease packed behind the pedal would do the same..............
Here is another twist to these cranks that I found: I noticed that some of these crank arms have a tiny hole drilled through the center of the pedal cap; possibly so as to prevent air pockets or excessive grease from popping the cap out? It would be my guess that this would have been the first revision to said crank arms.
Ted E. Baer Cool with a clear blue sky in Palo Alto, CA