Found something that might be a bug.
I was exporting a video of a scene but the result didn't show everything.
It seems as if images which have been invisible at the beginning of the animation (and become visible somewhere in the timeline) stay invisible in the video when exported.
I tried AVI as well as MOV ... even different settings didn't change anything.
Switching images did work fine with a shorter/smaller animation on a character when exporting a video though.
So maybe it depends on the size of the gfx or the length of the animation...(???)