in the changes view the activities that have checkouts in the current view and the activities set in any view are shown.
if the displayed activity is unset in the view, and the different activity is set, the new cl appears in Changes view, but the one that has been active before also stays.
This always appear for activities set in different views (since they usually appear empty in the view), but also can be recreated for activities in current view: check in the files from current activity, so that it becomes empty in Changes view. Externally set different activity for view --> new one appears, old one doesn't disappear.
These activities stay in view forever until you manually delete them - synchrinize activity action doesn'y help.