It all started with the realization that the glassware sculpties I had turned to flexi were displayed as flexi non-sculpt prims in the regular viewer. (I had left them that way thinking that in the regular client they would show as regular, non-flexi sculpts as usual.) In the edit window I noticed the flexi option not greyed out so I un-checked it right away on a few prims - and now the fact that they vanished from my view at that point didn't bother me, because I was editing from a distance and prims often are not visible from a distance. Only after I had changed a couple glasses to ghosted prims I realized what I had done! The prims were still "there" but invisible, for any avatar and any viewer. They were accounted for in the land's prim count, and one bumped into them. But they were also not selectable, so they were not just normally invisible but ... ghosted. ... So off I sent a support ticket requesting a region restart. Which didn't help. It took me a few days to come up with a way to remove those prims: I logged in with the non-graphical SL client metabolt ... which has a feature showing a list of all objects nearby - this way I could find the items turned ghost and remove them. Phew! I closed the re-opened support ticket, sharing my solution, LL didn't have any further ideas to help me anyway it seemed.