AutoCAD 2013 :: How To Apply Textures Of Individual Walls To Wall Faces

I cannot seem to find out when and where it's ocuring. I took measurements of a large room and modeled it in Autocad 2014. The solids I used are rather simple, mostly just boxes with some boolean unions and substractions here and there. I then took pictures of every wall, perspective-corrected them, imported each of them to Autocad as material, assigned the real size to the picture material and applied those materials to the corresponding wall faces. Planar mapping proved to be adequate in all cases and mostly mapped correctly on the first go.

The project was completed and saved. To my horror most of the material mappings had just gone the next time I opened the project. It was just as if I had never applied any material mapping or texture to the faces.

After partially appliying the damned material mappings and materials (textures) again I tried to determine under what circumstances the mappings get lost. Its not allways the same walls. The bug seems to occur randomly on various geometry and at various times. Sometimes the mappings get lost after opening the project, sometimes the get lost on the fly when isolating (hiding) geometry. There is no way I can get the room to look as I want it to look as there will allways be some wall that has become default-grey again, randomly (either while working or after opening up the project again).

I really expect Autocad to be rock solid after so many program versions. Did I do something wrong? How would you go about applying textures of inividual walls to wall-faces? Or is Autocad just crap regarding heavy use of textures because that is not the average use-case?