Description of feature:
This can happen with a migrated database from Ejabberd for example, and there is already a warning, which should be replaced with the removal of the self-contact.
Thanks. Merged as https://hg.prosody.im/0.10/rev/8b5d846dc664
I /think/ these were originally saved as part of normal roster storage, but the switch to map stores made it such that only changed items were stored in most cases.