Badmouthing between POIs

[Physwimic]

Hopefully you guys can give me some good advice. I was at an interview weekend, and a professor there told me about one of his former post-docs who is one of my POIs at another school. He informed me that the post-doc had agreed to move on to other topics, and then returned to here old project after that failed and scooped a grad student still working on the project. Even worse, he wasn't even informed that the post-doc had returned to the question. This is obviously, if true, really bad form and a real black mark on the POI. But there is a degree of bad mouthing that happens between schools at these interview weekends. I kind of want to give the post-doc now POI a chance to defend himself as there might be another side to the story, but I also feel it might be a bit rude to bring it up. Does anyone have advice on how to deal with the situation?