Got the following error importing this discogs release http://www.discogs.com/release/1167884
using http://userscripts.org/scripts/show/36376 :

"Error: An artist is required on track 1, An artist is required on track 2"

As you can see, seeded parameters are the following ones:
<form target="_blank" method="post" action="http://musicbrainz.org/release/add"><input type="hidden" name="name" value="Le Chat"><input type="hidden" name="country" value="FR"><input type="hidden" name="date.year" value="1976"><input type="hidden" name="labels.0.name" value="Barclay"><input type="hidden" name="labels.0.catalog_number" value="620 175"><input type="hidden" name="artist_credit.names.0.name" value=""><input type="hidden" name="artist_credit.names.0.artist.name" value="Weyman Corporation"><input type="hidden" name="artist_credit.names.0.join_phrase" value=" "><input type="hidden" name="mediums.0.format" value="7" Vinyl"><input type="hidden" name="mediums.0.position" value="0"><input type="hidden" name="mediums.0.track.0.name" value="Le Chat"><input type="hidden" name="mediums.0.track.0.length" value="4:24"><input type="hidden" name="mediums.0.track.1.name" value="Kumbayero"><input type="hidden" name="mediums.0.track.1.length" value="4:58"><input type="hidden" name="edit_note" value="From http://discogs.com/release/1167884"><input type="submit" value="Import into MB"></form>

mediums.n.track.artist_credit are NOT seeded, because they're equal to the release one.
This was working fine yesterday, so maybe it's related to commit 3434fcf33f7ee4c429e7e30ab3563dfbd0207f32