See thread on samba mailing list: https://lists.samba.org/archive/samba/2020-February/228153.html
Issue was reported by Alexander Harm. Thanks for reporting it and so making Samba better!
I've added tests at https://gitlab.com/samba-team/samba/-/merge_requests/1128 with a local originating update (which isn't the same thing, but is as good as I can trivially) and can't reproduce what I thought was the issue here. Sorry!