Populating surfaces with geometry

Hi,

I have a series of interior surfaces that I wanted to populate with geometry (beds, computers, cabinets etc.) - there are a few issues I am running into.

They work fine for single surfaces, but for some once you add in multiple surfaces to the definition it goes haywire and connects everything to everything else.

Another problem I am encountering is that the geometry appears on the wrong side of the surface - flipping the surface does nothing, and mirroring only works when I have a single surface in the definition - using multiple causes the geometry to move away from the surface unexpectedly.

Any help would be great,

Thanks

Carl