Why does WAITFOR (RECEIVE FROM QUEUE) show up in the monitor incorrectly?
Because is a DELETE. RECEIVe is just syntactic sugar for something like

DELETE from queue
OUTPUT DELETED.*
WHERE status = &lt;receivable&gt;;


If you enable retention then is an UPDATE, and will show as an UPDATE. There are some details, like how conversation group locking is done, how the proper message ExactlyOnceInOrder semantics are ensured and the syntax tree of RECEIVE is not truly possible to be built in T-SQL. As I said, details...

Is no coincidence I recommend in Using Tables as Queues to use the OUTPUT clause of DELETE to 'dequeue' from a table...