Distribution groups are bugged for rules
If you have a DG in office 365 and then if your owa create a rule for emails from that group to go to a particular folder, it will also send emails from any members of that group into that folder. So the rule gets applied to members of the group and not just emails from that group address. This only happens on Distribution groups not 0365 groups. I didn't see a section for Distribution groups so I posted here.