Hello Thomas,
You can't have controls overlapping each other on the virtual console (in either the CODM or the 'full' ODF format) -- that isn't supported. (Supporting layered/3D controls would add run-time overheads.) Each control needs to occupy its own distinct space. Transparency masks can only be used in order to allow the (fixed, static) background image(s) to show through.
Does that explain it?