Strange Linked Block Material Behaviour

Hello,
I have this file that has been have some strange behaviour with te Blocks materials.
We have a few building in a masteplan that share a bunch of materials. One thing that we asked in the past was to edit or assign materials to referenced blocks, but that - as far as we know - is not possible yet.

In this file, I want to load a Block Linked block as a Reference.
The original file looks like this:
image
When I load it in this file it looks like this.
image
When I load it in a new file it looks normal.

This happens with several blocks within this file and with several materials. I can identify the materials that are wrong in this file (some how the material is local to the host file)…
image image
and if I replace one of them with the correct version…
image
… it works
image

However, when I save, close and reopen the file not only the materials that I updated go back to a strange color, but even the one that I did not updated changes to still another color. Neither of these material are in the child file nor in the host file.
image

To top it all up, just saving, closing the file and reopening it, reverts back to the “original” wrong colors.
image

Again this is not happening only with these two materials, but with more in the scene.

Since we are talking about a very large file with several linked large files, I really cannot post an example and as mentioned, when I load the child file to a new file it seems to work.

Any ideas?
N

It now started to happen in another files. Could be related to AutSave rocovered files?? but why doesn’t it save the materials after the they are changed?
After opening
image

After reassigning a bunch of materials
image