Same contact appearing multiple times

I’ve arranged my contacts to different groups in MSN. Now, there is a strange thing with one contact – he is appearing in every group :confused: If I delete him and re-add, not putting him to any group, his name is appearing only once. But as soon as I group him, it’s in every group again. Anyone knows how to resolve this?

Edit: found a solution – somehow groups did get messed on my hotmail account, did dete double contacts/groups there and the problem did dissapear.