Yeah, I immediately CD-ed him on the spot. I was truly horrified since that was the first time that has ever happened.
My males normally don't fight and live together peacefully even with new comers.
Heck, one time I even had a "gang bang" with no hostile aggression. I used to put extra grow out males in with my breeder males to save space. They got along swell. I never did anything special for introductions. I just put them in and left. No problem. And one time, I miss sexed a female and threw her in there too. She grew to sexually maturity and all the males took turns breeding to her one after another. I was so surprised when I saw that.