The duplicate manager in darktable is a great way to explore multiple ways to process an image. However, it’s very easy to accidentally start working on the original or a duplicate that you don’t want to change.
I ran into this last night when doing an edit for the Help me stop fiddling with this Play Raw. Fortunately, because it was a Play Raw, I could go and re-download the OP’s xmp file. Had it been my own image, I could have lost a lot of work.
I think it would be a useful to have the ability to lock/unlock a version in the duplicate manager. I didn’t find anything in the manual mentioning such a facility. If the developers agree that it would be useful, I’ll open an issue on Github.