I had an odd occurence in this area.  The other night, for no reason, PP2010 rendered my character's texture as the background image.   There were no props involved at the time, as I was doing a test render on the character herself.  When I left render window, the proper background image returned and was visible.  I haven't since been able to reproduce the problem.  Just thought I'd drop that in since it was a possible topic add-on.