convert's playlist option uses original extensions

Problem

Running this command in verbose (-vv) mode:

$ beet -vv convert -m test.m3u lifelight
user configuration: /home/leo60228/.config/beets/config.yaml
data directory: /home/leo60228/.config/beets
plugin paths: 
fetchart: google: Disabling art source due to missing key
fetchart: lastfm: Disabling art source due to missing key
Sending event: pluginload
library database: /home/leo60228/.config/beets/library.db
library directory: /home/leo60228/Music
Sending event: library_opened
Parsed query: AndQuery([OrQuery([SubstringQuery('artist', 'lifelight', fast=True), SubstringQuery('title', 'lifelight', fast=True), SubstringQuery('comments', 'lifelight', fast=True), SubstringQuery('album', 'lifelight', fast=True), SubstringQuery('albumartist', 'lifelight', fast=True), SubstringQuery('genre', 'lifelight', fast=True)])])
Parsed sort: NullSort()
RichaadEB & Cristina Vee - Lifelight (English Version) - Lifelight - English Version
Convert? (Y/n) 
Parsed query: AndQuery([NoneQuery('album_id', True)])
Parsed sort: NullSort()
Parsed query: AndQuery([BooleanQuery('comp', 1, fast=True)])
Parsed sort: NullSort()
Parsed query: AndQuery([OrQuery([SubstringQuery('artist', 'Necrozma', fast=True), SubstringQuery('title', 'Necrozma', fast=True), SubstringQuery('comments', 'Necrozma', fast=True), SubstringQuery('album', 'Necrozma', fast=True), SubstringQuery('albumartist', 'Necrozma', fast=True), SubstringQuery('genre', 'Necrozma', fast=True)])])
Parsed sort: NullSort()
Parsed query: AndQuery([OrQuery([SubstringQuery('artist', 'Necrozma', fast=True), SubstringQuery('title', 'Necrozma', fast=True), SubstringQuery('comments', 'Necrozma', fast=True), SubstringQuery('album', 'Necrozma', fast=True), SubstringQuery('albumartist', 'Necrozma', fast=True), SubstringQuery('genre', 'Necrozma', fast=True)])])
Parsed sort: NullSort()
convert: Encoding /home/leo60228/Music/RichaadEB/Lifelight (English Version)/01 Lifelight - English Version.flac
convert: Finished encoding /home/leo60228/Music/RichaadEB/Lifelight (English Version)/01 Lifelight - English Version.flac
Sending event: write
Sending event: after_write
Sending event: after_convert
convert: Creating playlist file /home/leo60228/TranscodedMusic/test.m3u
Parsed query: AndQuery([NoneQuery('album_id', True)])
Parsed sort: NullSort()
Parsed query: AndQuery([BooleanQuery('comp', 1, fast=True)])
Parsed sort: NullSort()
Sending event: cli_exit
playlist: Updating playlist: /home/leo60228/Playlists/Shuffle.m3u

Led to this problem:

$ find TranscodedMusic/
TranscodedMusic/
TranscodedMusic/RichaadEB
TranscodedMusic/RichaadEB/Lifelight (English Version)
TranscodedMusic/RichaadEB/Lifelight (English Version)/01 Lifelight - English Version.opus
TranscodedMusic/test.m3u

$ cat TranscodedMusic/test.m3u 
#EXTM3U
RichaadEB/Lifelight (English Version)/01 Lifelight - English Version.flac

Setup

• OS: Linux (NixOS 25.05)
• Python version: 3.12.10
• beets version: 2.3.1
• Turning off plugins made problem go away (yes/no): no

My configuration (output of beet config) is:

# --------------- Plugins ---------------

plugins: edit playlist fetchart substitute mpdupdate replaygain convert info
replace:
    '[\\/]': _
    ^\.: _
    '[\x00-\x1f]': _
    '\b: ': ' '
    ':': '-'
    '[<>"\?\*\|]': _
    \.$: _
    \s+$: ''
    ^\s+: ''
    ^-: _
playlist:
    auto: yes
    playlist_dir: ~/Playlists
    relative_to: library
    forward_slash: no
fetchart:
    sources: [filesystem]
    auto: yes
    minwidth: 0
    maxwidth: 0
    quality: 0
    max_filesize: 0
    enforce_ratio: no
    cautious: no
    cover_names:
    - cover
    - front
    - art
    - album
    - folder
    store_source: no
    high_resolution: no
    deinterlace: no
    cover_format:
    google_key: REDACTED
    google_engine: REDACTED
    fanarttv_key: REDACTED
    lastfm_key: REDACTED
paths:
    default: '%substitute{$albumartist}/$album%aunique{}/$track $title'
    singleton: $artist/Non-Album/$title
    comp: '%substitute{$albumartist}/$album%aunique{}/$track $title'
substitute:
    ^nightmargin.*: Nightmargin
    "^\u98EF\u5409\u65B0$": Spike Chunsoft
replaygain:
    backend: ffmpeg
    r128: ''
    overwrite: no
    auto: yes
    threads: 24
    parallel_on_import: no
    per_disc: no
    peak: 'true'
    targetlevel: 89
    r128_targetlevel: 84
convert:
    auto_keep: yes
    copy_album_art: yes
    dest: ~/TranscodedMusic
    embed: no
    never_convert_lossy_files: yes
    hardlink: yes
    format: opus
    formats:
        opus: ffmpeg -i $source -y -c:v copy -acodec libopus -ab 192k $dest
        aac:
            command: ffmpeg -i $source -y -vn -acodec aac -aq 1 $dest
            extension: m4a
        alac:
            command: ffmpeg -i $source -y -vn -acodec alac $dest
            extension: m4a
        flac: ffmpeg -i $source -y -vn -acodec flac $dest
        mp3: ffmpeg -i $source -y -vn -aq 2 $dest
        ogg: ffmpeg -i $source -y -vn -acodec libvorbis -aq 3 $dest
        wma: ffmpeg -i $source -y -vn -acodec wmav2 -vn $dest
    no_convert: Necrozma
    pretend: no
    link: no
    threads: 24
    id3v23: inherit
    max_bitrate:
    auto: no
    tmpdir:
    quiet: no
    paths: {}
    album_art_maxwidth: 0
    delete_originals: no
    playlist:
mpd:
    host: localhost
    port: 6600
    password: REDACTED
edit:
    albumfields: album albumartist
    itemfields: track title artist album
    ignore_fields: id path