Dottyback decor

So, new thing going on in the tank. My Neon Dottyback is picking up big pieces of the substrate and swimming it up to the top shelf and dropping it off there. Any idea as to why? It's a little annoying as some of the pieces end up falling onto a coral in the sand bed but other than that everything is fine in the tank.  

He is the weirdest fish! Now he is loving on my purple star polyp island. I don't get it. I'll bring the video I just took of him. He's been doing this for days now. He'll swim through the middle of the rock, then it looks like he's rubbing his whole body against the polyps like he's trying to tickle himself.