[BUG] PasteUpMorph becomes a Sketch (Etoy)

When a Playfield is told to "look like" another morph it becomes a
SketchMorph. I'd expect it to just change its appeareance. That is, it
should change its sticky background morph to look like that other Morph. 
This would be consistent with the fact that I can just paint on it via the 
halo, which actually paints onto the background morph.

I'm not quite sure where to hook into, so no fix yet.

-- Bert