There's also been some changes in how "partial" MAT poses work. P4 (at least) allowed a MAT posefile that might just change the diffuse color, without affecting the texture being applied, so it could do things like alter skintones. P5 loses the texture file. Also, a MAT pose which includes materials that are not on the target will still add those materials, and there's no easy way of getting rid of them. A P6 Material Collection in the same situation will trigger an "are you sure" query.