I didn't know about pressing "L" that fixes the issues but removes all lighting torches all work also casting the correct colour of light. The drivers have been updated to the newest ones possible (but over a year out of date) and there are no newer versions.
If enabling a light fixes the problem, it's definitely a shader problem, so I guess it's eventually a driver bug (since it's the first time this problem occurs). We will have a look if we find a workaround.
Did you try another driver version (not necessarily the newest version, you could try to install a previous version)?