Just fixed the PostgreSQL error and tested it locally – should all work fine now and the fix will be included in the next release 
Turns out the database needed a safe=True to ensure that tables weren’t re-added. While debugging, I also discovered a PostgreSQL-specific inconsistency with how BlobFields are interpreted (“bytea” instead of “blob”, see here for details). Those fields are used for project meta and examples, i.e. dumped JSON strings. So Prodigy now handles those correctly as well.