Recently notmuch-restore gained the option to restore configuration
information (--include=config). One potentially surprising aspect is
that it behaves as if --accumulate was given for config data, even if
replacing all the tags on each message. To be precise, if some config
data is in the database, and not mentioned in the input to restore, it
will still be there afterwards. I lean towards this being a feature
rather than a bug, since I think it would be even more surprising to
have the config data wiped out. I guess not many people use this feature
yet (or even know about it), so we can still change this behaviour. Or
at least document it better.  A lawyerly reading of the docs is
consistent with the current behaviour, but it is a bit misleading (as
with all good lawyerly things).

d