When pug-tanking lowbie dungeons for a friend-
We smash through the place. Kill the last guy. Everyone loots, I wait a tic for people to equip upgrades and whatnot, then requeue.
And someone. ALWAYS. Cancels the queue, THEN leaves. 
Sometimes more than one person. Cancel, leave, cancel, leave.
You can just leave. You don’t have to cancel the queue! 