Ah,.. I see. Yes, in some ways, it has happened to at least one or two of my lanterns. Not while they were running but they got partially detached from under the cap during fettling work. The discs were made of steel. They can rust and oxidize pretty badly. Apparently, they got compromised along the edges with time. For mine, it was likely that substantial rusted material had being removed during citric acid soaks. Hence, became rather loose-fitting in the cap. Repeated lantern operation cycles can also deform or slightly alter the geometry of the lipped-folds of the hood caps, leading to a loosened hold on the disks.
Another collector here in Denmark had the top cap pop off with a bang while the lantern was running. It had just been cleaned before being used. What happened was water was still between the hood and the cap and when it evaporated it created enough pressure to pop off the cap. This can probably happen with the steel disc as well.
