If you used a query to target devices then when the task is run the query is also run and the individual devices are listed. If you restart the task the query should be run again at that time, so a current list of devices that meet the query criteria are added as individual targets. Now, if you delete a device then it can only really be removed from the list by also removing the query it came from. Removing the query it came from will also remove any other devices that came from the same query.
That's the gist of the message.