They do say it twice, and you should read it back twice.
"Caledonian 123, behind the landing 747 on short final, cross runway one-two-left. BEHIND"
I don't like the practice myself either. It does little to speed things up, and I don't trust the other pilots to follow the instructions.
When the controller sees the arriving aircraft pass the threashold, then they should issue to the "Line up and Wait" clearance to the next guy in line.
The problem in OMDB is that it's short-staffed. So the controllers are too busy to watch where the planes are.