I too have witnessed this in my tank. My Jag builds the nest and he chases away every other fish (including the female jag) from the nest and if he gets any trouble from anyone he attacks. I have seen him attack my oscar so I know he is not afraid of it, but he WILL NOT chase away the albino tiger away from the nest. The two follow each other around the tank all the time, rub against each other and are always nice to each other now.
I am not saying they are mating I am just sayin hey man I have seen the same thing lol
Sorry if this post was totally useless!