I haven't experienced this firsthand but I've seen the polymorph effect happen to an already polymorphed PC, giving it free hps from time to time.

I thought this was intentional? It flashes and heals, perhaps like 10 hp or something, depending of something :P

It's a bioware bug. It's a server save. It demorphs you to save you with all your gear and proper stats, then remorphs you, reapplying the temporary hp.

I took a stab at fixing this known issue in v823.