I'm following the Spitfire tutorial (very cool by the way) but I don't understand how the instructor is moving between sub div polgons and back again?

When the instructor is attaching the wing to the fuselage he uses the turn polys to sub div, this I get. But then he seems to click on the sub div to polygons shortcut to jump back to the model BEFORE it was sub divided, kinda like a undo. This I definitely don't get!?

When I do this my object stays sub divided (the polys change slightly too) and in my channels it changes to,subdtessShape1. Why is this not working like the instructors? Ie, simply turning off subdiv like it was a mode?

EDIT: This happens around 10:34 in part 3 and another good example of it is at 21:46.

Please help?