Thanks, Bruce
Yes, in view only mode. My thinking was that even though a form is in view only mode it still shares the same form queue as an editable version of the same form on another tab.
But in thinking about it more, if the session value is only created/deleted in editable forms, a view only instance of the form could not be opened if the editable form had not been saved or cancelled. And if an editable instance of form is opened in another browse tab after a view only instance was opened, none of the changes made to the editable form will be saved to the view only record, so it doesn't matter.
Not exactly great UI, but it will have to do.