UI Artifact

Hello,

i have this kind of strange UI displayed when the game starts.
i'm wondering what can cause this.


it is like if a panel was not fade to 0, but i tryed to deactivate one by one all the UI object and it continue to make this dark rectangle during some times. then it can suddenly disappear.

when i deactivate light this artifact is disabled, if i keep the main light off during enough time, when i reactivate it, the artifact is gone.

i also deactivated all camera effects, without result.

so i have no idea what causes this problem and if someone else go this too.
and the best is that if i start the game and only have the main GameObject activated for the UI, it is still making this rectangle over.

see the image below in full size


any help is welcome.

 

well, i finally fund the problem comes from a second camera attached to the player witch has a bad setup.