Apologies if anyone else has pointed this out or queried it. It looks to me like the MT5 files held in the libraries:materials folders will replace MATPose files. Its slightly perverse that this library only appears when you are in the Materials room, it makes saving a good thumbnail a two stage process. If for example you want to save a series of clothing textures for a particular clothing item_ save the textures to a named texture library_ you'll get a thumbnail of the jpg texture map (not much use)_ exit to the pose room and then render a 91x91 png thumbnail and save it to the material folder you created, with the same name as the texture png it corresponds with. You now have a nice material preset with the old style MATPose format without clogging up your Pose folders.