Well that is not common place, because as I explained before, the 'correct' way of twisting the belt on a Senior is the exact 'incorrect' way of twisting it on a Junior. Both cleaners have a clockwise spinning pulley, but the roller on the Junior is designed to turn the opposite way to a Senior, hence the need for the twist to be on the opposite side.
On a Senior, the correct twisting of the belt actually goes against the grain, so to speak, of a clockwise spinning pulley and this is why the cap on the pulley is so large when compared to a Junior; it serves to keep the belt in place. Installing the twist on the wrong side of a Senior belt is to have it running like a Junior, and is essentially going with the grain, leaving it even less likely to roll off than if it was twisted as per the Hoover diagram.