I noticed, that if you add a displayobject with 3D properties as child to another display object, then all other childs of this parent will also have theyr transform.matrix3D property set, although they don't need it.
Does this mean that these clips also will be cached as Bitmap, although it's actually not needed?
Can someone who understand the internal workings explain when and under which circumstances exactly a displayObject is cached as bitmap (in relation to 3D properties, not to .cacheAsBitmap property) as well as when and under which circumstances this cache gets updated?
Forwarded to our 3D team for their review.
my conclusions were wrong.
it's actually this problem: http://forums.adobe.com/message/4235974#4235974 that caused the strange behaviour i was observing. adding a 3d child does not make the other children of the parent 3d objects.
You already got your answer, but I'll chime in with the answer from engineering: Only the top level DO is cacheAsBitmapped. All children need matrix3ds to make the math work right. That doesnt mean they need their own offscreen bufer.