Materials and textures go missing after Git commit

We have a peculiar issue with our game. We are two developers and a graphical artist that collaborate on a project using Git.

We have now multiple times experienced that after the graphical artist has committed some changes to some models, the materials, sometimes the textures, go missing on these objects. All materials and textures exist in the project, but the link in the model to the material, and the link to the texture in the material, are missing. Everything looks fine on the graphical artist's machine.

Even if the graphical artist try to delete the materials on his machine, create some new ones and link those to the model, the link is STILL not existing after we pull it to our machines.

The only solution is that one of us developers re-make the materials on our machine, and commit this. This causes them to go missing on the graphical artist's machine, but if he then resets his Git repository and re-pull everything, it works on his, suggesting that the GIT version is correct, and it is something on his machine that goes bad.

We are all on Windows 7 with meta files for version control in the Project Settings > Editor.

Does anybody have an idea what is going on here?

Regards, Vicas