A field value is currently not in any group. What happens when you try adding it to an existing group?

Select an answer:

It is still kept under the "all" list, and a second copy of it is placed under its new group.

It is removed from the "all" list, and placed under its new group.

Actually, it is not possible to add a field value to a group that already exists.

It is removed from the "all" list, and will not show under any group.