I had a user on my Discord server report very odd behavior from dgVoodoo when used with the game Pro Race Driver (aka TOCA Race Driver) - he said that when dgVoodoo is set to do the rendering, every time he launches the game his desktop wallpaper switches to slideshow mode and starts flipping through the available images. He checked the "pass through to real DirectX" option, and the bug stopped occurring.
I asked him to give me a dxdiag so I could report the bug, thanks Dege!