Ok, I just figured out that when I save the rendered view in a bmap like that:

camera_scene = bmap_createblack(screen_size.x, screen_size.y, 24);
camera.bmap = camera_scene;

And then use "camera_scene_bmap" within the shader instead of "TargetMap" everything works fine.

But shouldn't be TargetMap set automatically?

I only add this single stage to the camera. I really can't figure out what's wrong here.

Any ideas?

Sascha.