I have a radio group of 3 tags defined in org-tag-alist: now. next, later. This tag group works correctly when editing the tags directly in the original org files or when the tags are edited individually in the agenda using ':'.

When editing tags via the agenda's bulk editing command, however, adding a tag from that radio group does not remove any pre-existing tags from that group.

For example, say an item is already tagged "now", and the tag "next" is added to it via bulk editing. The expected result is that the tag "next" is added and the tag "now" is removed. Instead, the result is ":now:next:", as the pre-existing tag is not removed. 

I have version 9.2.3

- Mark Kerr