They still have feelings for them. I left my husband in Sept and we together for 7 years. I couldn't care less if he dated one of my friends. I would want to warn them about him first but when you don't have any feelings left for a person there is nothing to get upset over.
I never got mad when someone dated my ex. If I didn't like the person then I was happy. If I did like the person, then I was worried. My ex was a horrible person anyway and never even TRIED to be with me. She looked at all the negative things; the stuff we weren't able to do together rather than the positive things (the stuff we were able to do together).