Given auto-stop is enabled, when I edit the duration and submit, then the audit log says I set it to 0 even though I set it to a non-zero number.

Given auto-stop is disabled, when I enable it, then the audit log has an entry with no diff.

I think what's going on is that the audit log entry for anything to do with auto-stop always shows it being set to 0. So disabling it appears to work because 0 is correct, enabling it has no diff because it was 0 before, and editing it has an incorrect diff to 0.