Surface Material problem

[capt.crayola]

I'm working in AutoCAD C3D 2013 and I have a drawing with several XRef''s, Data references etc. and recently the file has been slowing down considerably.

One of the first things I did was to purge, and when I did I noticed that I had a bunch of surface materials loaded and available for purging (see attached). I purged, saved and re-opened my file, and the materials were back. The materials don't reside in any of the XRef or Data refernced drawings, just the one that I'm currently working on.

Second step was to WBLOCK my drawing into a new one, but the materials followed into the new drawing. As I stated above, I can purge them, but am concerned that they're not really gone as they keep re-loading, and are part of the problem with my file slowing down.

Has anyone experienced this problem, and if so, does anyone  have any solutions on how to remove them?

Thanks,