Hi ya
Been working on various texture problems for a few weeks now, but the last ones seems to be retention of textures in the cache, which im quite sure is a bug, anyway in my troubleshooting i found that the probable cause is that textures dont seem to be overflowing from the texture cache in memory to the one on the harddisk, so for people using the option of a small texture cache because they have less than 512Mb of ram (Preferences > Adv. Graphics > Texture Cache) then try switching it to Large, this seems to allow alot more textures to load in the scene and if you are low on ram it will only be swapping them to virtual ram instead.
So no guarantees but hopefully might help and if it does then bug report it like i have.