OK, I'll try again. This would take about 30 seconds for someone to try. Please confirm or deny this bug for me.
1. Place a video into the comp.
2. Select new camera.
3. Make 3D
4. Rotate the view so that you can see behind the video.
5. Use the paint brush and paint a scribble.
6. Move the scribble in 3 dimensions so that it is clearly behind the video.
7. Rotate the view so that the video covers up the scribble.
8. Make sure the opacity of the video is 100%.
9. Make sure the opacity of the layer is 100%, and blend modes are all "normal".
Can you see the scribble through the video?
I do, and it doesn't make any sense to me.
Please, I beg anyone. Please tell me if you repeat this problem, or if it is just me.
It sounds like the group contents are being rendered in layer order, instead of depth order. This can be done manually, but is sometimes automatic. What kind of paint stroke are you using? Is it a 3D stroke (i.e. Local 3D checkbox is enabled in the stroke's Shape settings)?