A nice bug combining all the broken features of blender: Particles, duplis and multiple scene dependencies. Fortunately this was solvable: Basically, we need to make sure derivedmesh for dupli instance is generated before obmat is overriden. This also makes sense, since no instance has "true" obmat apart from original. Lazy initialization of derivedmesh just does not work here (or it -does- work but first use should be before instance drawing). Fingers crossed nothing else breaks after this...