When you removed all the people from a group in the raid tool it removes the "group leader" flag for that person however it still counts them as a group leader and does not allow you to insert people into that group unless you first re add the original group leader. For example. I have a raid of 12 groups. I disband everyone from the group 6-12. When I go to place people back into those groups it will not allow me unless I move the original group leaders back into the group first. However those members no longer have the "group leader" tag to know who is taking up that spot in the raid tool.