What is the new shaded area called and how can I turn it off?

When the sketch creates a watertight boundary we get this new shaded area.  Cute.  However, try to rubber band a selection within this area.  The WHOLE mess drags and destroys the geometry.  Yes, I know the sketch is not fully defined.  I don't want it locked yet.

Anyway, what is the name of this new feature so I can find out how to disable it?

Many thanks

Carter

PS.  Oops sorry.  Using 2017 SP 1