I eventually found the culprit. A small E that had a molt deformity. The last segment of his rear right leg is upturned funny, and doesn't appear to be functional. And the back right side of his carapace is folded up weird. I've circled the two spots in the picture.
Because of his deformed back carapace, the shells probably don't feel very comfortable on him. So that's why he was constantly dumping his current shell and trying out another one.
Well, then one day I find him in the water bowl, without a shell, and figure he's passed. So I pick him up, and nope! He springs to life and flails around. I originally kept giving him new shells to try, but he never lasted in them.
Eventually he just dumped wearing shells altogether, and has been living naked in my tank ever since (about a month now). And he's still very active. Not a sign of lethargy or sickness. So hopefully he should come out of his next molt OK. He spends a lot of time dunking his butt into the water though, as would be expected.
I know there's some poeple who collect pictures of molt deformities for research, so I thought they'd be interested. And I thought it was also good to show proof that crabs can survive without shells for long periods of time. Crabs don't necessarily die because they left their shell. Crabs usually are sick anyway first, and then leave their shells because of their sickness.
very weird....how is it that the other crabs don't pick on him, I wonder? So, in order to correct the deformity, he would have to molt, but will LHC molt naked 
? I guess he'd almost have to. Keep us posted, please.
I always panicked, but now I have more hope with naked crabs..actually it only happened to me once in a shell fight.
Thanks for posting!
