I thought my case was rare, but looks like others are having similar problems. My power blue tang has been a model citizen for the last year or so, until recently I noticed the tips of my monit's and acros going white. After examining it closely, I discovered that it the PB that was nibbling on the tips. It started on an encrsting monti and then moved to a couple different millipora colonies. Currently I can see about four different colonies that has partial white tips. Nothing major that would kill the coral but it does damage it to the point of stunting the growth causing lost of color to the damaged area.
Like many of you, I don't know why it picked up this new habbit. It's well feed and is very plump. My only reasoning is that it only does this when it has the "munchies" or when it is bored. I figured since I have a tank full of SPS, a few tips wouldn't hurt. I love this fish too much to try and remove it ( don't know if that's even possible). This problem has been onging for about 3 months and by now I think it is safe just to let nature take it course.
I also have a Sohal and Naso that are both doing fine....no bad habbits, atleast not yet.