Crash on load unless Library is deleted (and Other Things)

Case 674292, Unity 5.0f2

Has anyone had problems with DX11 mode?

After switching to DX11, my Game view went black.

Switching out of of DX11, everything stayed black.

Turns out this is a problem with Depth Only cameras (in my case a UI camera (not Unity UI, just a makeshift setup) and HDR mode on the main camera.

- Disabling HDR solves the black screen, but no image effects (DOF etc) work.
- Disabling the UI camera gets rid of the black screen and allows HDR and image effects to work.

Also, every time I close the project, I have to delete Library otherwise it crashes (at the point it's opening the scene). All of the above post-DX11 switching bugs remain.

I've cleared the GI Cache, tried setting a different scene as the last opened:
- an Empty scene works, and other scenes can be loaded fine after
- a scene that was saved post-DX11 switching doesn't (crash on load)
- a scene that's not empty but wasn't saved since the DX11 switch works, but closing Unity takes about 15 seconds instead of instant close.

It's all a bit mash. Does any of this sound familiar to anyone?

The problem is, there is so much is going on here that's it's hard to see where one bug ends and another begins or how they may or may not be related.