Same beatmap song plays twice during gameplay (two Track instances)

[1231234567812]

Symptom

During gameplay, the same beatmap song plays twice simultaneously. Normal in song
select / menu, but as soon as gameplay starts there are two identical tracks.

Confirmed as two instances of the same song (not music + hitsounds) by setting
AudioOffset to 500ms — the two copies become clearly audible half a second apart.

Evidence: the same beatmap is set twice in the same second

From runtime.log:

2026-10-06 17:26:16 [verbose]: Game-wide working beatmap updated to xi - Blue Zenith (Jepetski) [Hyper]
2026-10-06 17:26:16 [verbose]: Invalidating working beatmap cache for xi - Blue Zenith (Jepetski) [Hyper]
2026-10-06 17:26:16 [verbose]: Invalidating working beatmap cache for xi - Blue Zenith (Jepetski) [Hyper]
2026-10-06 17:26:16 [verbose]: Game-wide working beatmap updated to xi - Blue Zenith (Jepetski) [Hyper]
2026-10-06 17:26:16 [verbose]: Invalidating working beatmap cache for xi - Blue Zenith (Jepetski) [Hyper]

Normal flow should be one updated per one Invalidating.

Present in every session over 7 independent logs:

session       updated  Invalidating  maps set twice
10-01 12:58        20           27                6
10-01 19:35        64           96               20
10-03 21:43         7            8                1
10-04 13:42         7           10                2
10-06 23:48         5            5                1
10-07 00:53        24           39                3
10-07 01:26         5            6                1

Suspected cause

osu.Game/OsuGameBase.cs guards against duplicate track adds with an identity check:

Beatmap.ValueChanged += b =>
{
    // compare to last beatmap as sometimes the two may share a track representation
    // (optimisation, see WorkingBeatmap.TransferTo)
    if (lastBeatmap?.Track != b.Track)
    {
        lastBeatmap?.Dispose();
        Audio.Track.AddItem(b.Track);
    }
    lastBeatmap = b;
};

If WorkingBeatmap.TransferTo produces two different Track objects while the beatmap
cache is invalidated/refreshed (as in the log above), the != guard passes both times
and both tracks end up in the TrackManager, playing simultaneously.

Already ruled out

• PipeWire-level duplication — pw-dump shows only 1 osu Stream/Output/Audio node
• Multiple osu! instances — only 1 process
• loopback / audio routing — none configured
• Multiple output sinks — only 1
• Beatmap background videos with audio — all 4 videos in storage confirmed to have
  no audio stream via ffprobe
• Hitsounds — BeatmapHitsounds = False, and both sounds are the same song
• Song select preview lingering — normal when not in gameplay

Environment

osu! version : 2026.921.0-lazer
OS           : Arch Linux
Kernel       : 7.2.7-zen1-1-zen
GPU          : AMD Radeon RX 5700 XT (Mesa 26.2.3)
DE           : KDE Plasma 6.7.5 (Wayland)
Audio        : PipeWire 1.6.9 (device = "PipeWire Sound Server")
Renderer     : OpenGL
ExecutionMode: MultiThreaded
FrameSync    : Limit8x
Ruleset      : mania

Repro

1. Launch osu!lazer
2. Pick any beatmap, enter gameplay
3. Two copies of the same song play simultaneously

Reproducible every session.
1791307559.runtime.log