I also have this problem. Preview texture come from previous projects which I have already deleted and not in my system anymore. Even I add 3 new materials. The same preview texture appears on the those 3 materials.It looks like I've found a workaround to this bug.
It seems to be a problem with the "+PRECOMPUTEDINVAVG" tag in the FLAGS file, as removing that tag also fixes the issue.
- Create Material (preview displays incorrectly)
- Assign it to object (apron, painted line, etc)
- Save Project
- Close Project
- Delete the new .FLAGS file in the materials folder.
- Open Project
- New Material displays correctly.
I will try your method tonight. Thank you.
