This specific bug involves a release with 2+ recordings where each is attached to a work, where one work has a lyrics language and the other does not.

For example, at the time I recorded this bug,

Picard settings: Enable track relationships.

Picard script:

$set(lyrics language,%language%)
$unset(language)

Use 2 FLAC files that have the properties of tracks 1-2 from https://musicbrainz.org/release/5643b133-055a-460b-a47a-03dd88e43882 - Cluster the 2 files, then Lookup the release.  This release has specific data seems necessary to reproduce the bug:

Work 1: https://musicbrainz.org/work/bd34eb48-506e-39fa-b890-6e63d02da39b?tport=8000 is "jpn"
FLAC file 1: Preexisting "lyrics langauge" tag that is "Japanese"

Work 2: https://musicbrainz.org/work/6f98f386-0bde-43c7-98b6-64c489ad6f48?tport=8000 has no lyrics language defined
FLAC file 2: Preexisting "lyrics language" tag that is "Japanese"

If I match files 1-2 to tracks 1-2 in this way, then this happens in Picard:

1. Select the release: "lyrics language" is incorrectly left in black text, even though track 1 would be modified.
2. Expand the release and select track 1 only: "lyrics language" is colored with the modified value "Japanese" -> "jpn"
3. Select track 2 only: "lyrics language" is left in black text; no changes.
4. Select both tracks 1-2: "lyrics language" is incorrectly left in black text, even though track 1 would be modified.