Unfortunately, this seems to be a problem with anything you hide, most common with the nasty white bath-towels we laughingly call cloaks. Anytime you cross a server, fly, join a scenario, etc, the armor bit you had turned off turns right back on. Mythic knows about the issue but they have given us no word as to when they will fix it. Soon, hopefully, cause it is indeed very annoying.
It could be worse for your little Shaman though. I saw a Shadow Warrior the other day who had insane hair clipping issues such as I didn't think this game had (not having run into hair clipping thru a helm before in WAR).