Interactive plugins (authorize and paypal ) must use 'manual'.
Some patches must be applied to lib/db.
http://moodle.org/bugs/bug.php?op=show&bugid=5941
Look: version.patch, lib_db.patch
Eloy, your question about enrol fields for interactive plugins were solved.
Now, we sure we never use authorize and paypal field for backup and restore.
Because manual is active and cannot be disabled when restoring.
Bug #5358 - Add support for enrol systems in backup/restore
http://moodle.org/bugs/bug.php?op=show&bugid=5358&pos=0