Thank you, Omar. It is a great video – when I watched it earlier today it helped me figure out how to override materials more easily and reliably. But then I got stuck on this reverting to default thing, which is stopping me from developing my library – I feel I need to figure out how to set it up from the beginning to avoid major rework later.
As for it being a bug, I could only find a few older reports that are mostly related to armatures and then one person with the same problem but no answer from 2 years ago. So if it is a bug it seems it’s been around for a while. I don’t know who else I could ask for confirmation since I feel quite intimidated by the bug reporting. But I will try the latest version, that can never hurt anything.