This has been a chronic problem for me as well - both with P7 & Poser Pro. 

I think IsaoShi had something when she said "..be sure that the textures are not loaded to more than one runtime."    Unfortunately, I have been sloppy with my RTs in the past.  I have loaded clothes and hair to more than one RT & then forgot which ones.  And I just don't have the time to clean them up and get my RTs in order.

Lately, I have been limiting my Library to only those RTs that are needed for the scene I am working on.  When I am finished with a scene I eliminate most of the RTs from the library and load only what I need for the next scene.  I think it is helping, but it is too soon to be definitive.