Can you give an example of the album that shows this behavior?
Regarding the version: you can go to %APPDATA%\Mp3tag\data\sources where
Cover Art#Discogs.src
Cover Art#Discogs Release ID.src
Discogs.src
Discogs Release ID.src
are the official Discogs sources. The version of Discogs.src that is shipped with the current Development Build is v1.09 (you can see this in the file's header).