1. Create and link at least 43 objects together, I used prim boxes.
  2. Select PBR material in the texture edit tab
  3. Drag and drop a material from your inventory onto the Material preview box
  4. Material will look applied. But It is not visible to anyone else. De-rezz and re-rezz (or relog), material will disappear.
  5. Unlink enough parts so you're at 42 or less linked parts
  6. Repeat the process - it will work now.
Tinting faces seems to also have a similar issue - the change it tint just does not apply.
Note: seems like number of faces matters too, if using mesh or different type prims you might need to link more or less objects to reproduce the issue.
Editing individual links or faces works fine.
Edit: 43 * 6 = 258... I bet it works with 255 Faces :D