When you open the searchable pull-down lookup list to select a Resource, Role or Team to a Task, the list always includes resources that are already assigned to the Task. When you select a resource already assigned, a toast error message appears: ERROR: Team member is already assigned to this task.
On later versions of Clarity the error is: PRJ-07251: Resource has already been assigned to the task
Release: 15.5 and higher
This issue is working as expected. The current implementation for this pull-down does not filter out staff that is already assigned to the task.
No option to work around the behavior is available.