Confirmed – renaming the external disk so it doesn’t begin with ‘media’ immediately halts the spurious importing. Switching back and forth between naming the external drive ‘media backup’ and ‘my media backup’ reliably starts/stops the errant behavior.
So … this is a bug: the configured path of a storage folder, e.g. /Volumes/media, will actually result in a wildcard match on /Volumes/media*.
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kobi