Right - so from what they've said, Motion only deals with simple raster layers in 8-bit files.  Useful to know.  They don't even support layer raster masks (which surprises me)!   If this is the case, it's going to be difficult to support Motion reliably without doing some work. (Seems to be the case when working in Photoshop also).  You can't use any effects, masks, or vector content.  You have to create your layers to be simple raster/pixel layers.   Does motion even deal nicely with Layer g