Multiple camera deferred HDR black screen?

Hi everyone,

I come here with a real annoying problem.

I'm working on a game with my team and we want to use two camera :

- Camera 1 : Render the level (Clear flags : Skybox | Depth = 0 | Deferred | HDR)
- Camera 2 : Render the UI (Clear flags : Depth Only | Depth = 1 | Deferred)

My canvas is in Screen Space - Camera rendered on the camera 2

The problem is that when HDR is toggle, the Camera 1 render is completly black but Camera 2 still render the UI on top. If HDR isn't toggle, everything works fine. The Camera 1 render the level with the Camera 2 rendering the UI on top.
I tried many possibilities like changing the depth, the clear flags, etc... but no way...

On internet, some post seems to say this is a "bug" that unity need to correct since Unity 4, some people find weird way to manage such situations with RenderTexture etc... but there is a cost in performance, so i would like to know if someone can clear my situation.

Thanks a lot

have a good day!