well its working on mine ( hence mentioning the firmware on it )
the screen shows the same sort of imageas in your video Marmad, when you first show the square wave. i can then get it to loose the left down trigger, and the counter (also with a T in the front of it, as I had the trigger on, and using the normal setting as per your DS2072 ) then goes squiffy. ie. its showing double of my function gen input. then tops out around the 40Hz on the counter, but 20Hz on the FG. going higher on the FG and the counter on the scope goes down ... not down to half, like you were seeing on the external trigger out, but down it goes. so 21Hz on FG shows 33.76Hz on counter ( that was one time i wrote down ) but not sure what timebase that was now.
ie wasnt using persistance vision, used vectors instead of dots, as only at low timebase where the dots mode usable on the 1052e for this test.