This appears to be a new issue: When querying discogs, in the usual way (i.e., discogs.src) the GET request to api.discogs.com is coming back with a 401 unauthorized, resulting in no cover art appearing in the result. The other data seems to be unaffected. I don't have any experience with oauth so this is where my contribution ends Here is an example capture of the relevant http reply:
GET /image/R-373924-1105126848.jpg HTTP/1.1 Host: api.discogs.com User-Agent: Mp3tag/2.58 Accept:*/* Accept-Encoding: gzip
HTTP/1.1 401 Unauthorized
WWW-Authenticate: OAuth realm="http://api.discogs.com"
Date: Fri, 14 Feb 2014 23:59:46 GMT
Via: 1.1 varnish
You must authenticate to access this resource.
Godspeed, good developers!