Darker Lighting in Extended mode vs Direct To Rift

I've encountered a strange bug where my app has significantly darker lighting when run in extended mode than when it is run in Direct To Rift or simply run on a monitor with a non OVR unity camera.

Here are two images to demonstrate the bug:

Standard unity camera on a monitor (this is also how Direct To Rift in "Direct HMD access from Apps" mode looks):

notice how the floor, towers and skybox are all clearly visible.

Now, here's how a comparable image looks when in extended mode:


Nothing is visible. Only the self illuminated materials and areas that have point lights in them.

The REALLY weird part is when in extended mode if I hit 'space' to bring up the Oculus frame rate counter OR move the headset out of the camera tracking volume (to bring up the yellow warning text) the brightness corrects itself and looks like the monitor / direct to rift version! As soon as I hide either of these overlays, the lighting returns to being really dark. This issue also occurs in the Unity editor in 'Play' mode (although looks fine outside of play).

This all seems to be a consequence of being in Linear lighting mode. When I switch back to Gamma, everything looks like the second, dark picture all the time. I'd rather not switch to Gamma just to get around this bug.

Thoughts? Has anyone encountered this or know what might be causing it? You can test it for yourself here.