0.4.3 disable mirror performance issue

With this new release, I noticed when you disable mirroring in app using the 'M' key, the FPS starts nose-diving, eventually dropping below 75fps (I turn off vsync to watch it drop), and then getting into judder issues. Turning mirroring back on makes it go back to the normal fps.

Anyone else have this issue? I'm running DX11 and 4.6.0b21 (4.5.5 equiv).

ccs