Wayland session restore doesn't work properly using fractional scaling (under KDE?)

mpv Information

mpv v0.41.0-920-gdd5d17d32 Copyright © 2000-2026 mpv/MPlayer/mplayer2 projects
 built on Aug  8 2026 22:56:30
libplacebo version: v7.360.1
FFmpeg version: n9.0
FFmpeg library versions:
   libavcodec      63.1.100
   libavdevice     63.1.100
   libavfilter     12.1.100
   libavformat     63.1.100
   libavutil       61.1.100
   libswresample   7.1.100
   libswscale      10.1.100

Other Information

- Linux version: CachyOS
- Kernel Version: 7.1.6
- GPU Model: NVidia 5080 RTX
- Mesa/GPU Driver Version: 610.57.04
- Window Manager and Version: KWin 6.7.4
- Source of mpv: CachyOS Repo (znver4)
- Latest known working version: n/a
- Issue started after the following happened: n/a

Reproduction Steps

Configure KDE to use fractional scaling. The example at hand uses 150% scaling. Define a Wayland session name in mpv.conf.

Keep restarting using the same video, since you expect mpv to restart at the last used window dimensions/width as before due to session restore.

Expected Behavior

The window to spawn at the correct size, not the reciprocal of 150%.

Actual Behavior

The window keeps shrinking at the inverse of the fractional UI scale. See example recorded here:

https://www.youtube.com/watch?v=GzJ25qQTnJE

First three attempts without Wayland sessions enabled. Then a Wayland session name gets defined and things start shrinking.

Log File

output.txt

Sample Files

No response

I carefully read all instruction and confirm that I did the following:

• I tested and confirmed that the issue exists with the latest release version or newer.
• I provided all required information including system and mpv version.
• I produced the log file with the exact same set of files, parameters, and conditions used in "Reproduction Steps", with the addition of --log-file=output.txt.
• I produced the log file while the behaviors described in "Actual Behavior" were actively observed.
• I attached the full, untruncated log file.
• I attached the backtrace in the case of a crash.

No source file or test is named. Start by reproducing the shrinking behavior with KDE fractional scaling at 150%, a Wayland session name in mpv.conf, and the same video across restarts; then inspect output.txt and the relevant Wayland session-restore handling. Done means repeated launches restore the correct window size rather than shrinking by the inverse scale.