Before commit 4f709dbfb45549b07afd5f636885a9d24946cc97, jack would use the most recently modified cached metadata (ie, jack.freedb or jack.musicbrainz), regardless of the default metadata provider. This behaviour is now broken when musicbrainz is the default metadata provider, yet jack.freedb is the only available cached metadata. Jack now creates an empty jack.musicbrainz which will then be selected because of its newer modification date, leading to failure.
Before commit 4f709dbfb45549b07afd5f636885a9d24946cc97, jack would use the most recently modified cached metadata (ie, jack.freedb or jack.musicbrainz), regardless of the default metadata provider. This behaviour is now broken when musicbrainz is the default metadata provider, yet jack.freedb is the only available cached metadata. Jack now creates an empty jack.musicbrainz which will then be selected because of its newer modification date, leading to failure.