Strange indeed. I have had it happen to different kinds of rabbitfish with two different kinds of tangs. I thought it might be common.

I just added a Foxface to my tank and the only one to take any notice was the Yellow Tang. She has tried to slice the FF a few times and was met with a bunch of spines. So far no damage to either one of them as they are not very aggressively going after each other, more like a half hearted posturing display. Leaving the tank dark all afternoon, hope it all works out.

My FF and SF Tang did the same thing; sparred like that for a few months. Now they're best buds. Follow each other around like a couple of puppies.

I have seen this behavior in my tank. My little Sohal will 'nip' at the spikes of my Foxface. It only happens once in a while and it doesn't appear that they are really fighting. I haven't noticed any damage either.