`sub-relaod` command may change the `sid` and `secondary-sid`

mpv Information

mpv v0.40.0-217-g0ac07305f Copyright © 2000-2025 mpv/MPlayer/mplayer2 projects
 built on Jul 22 2025 00:10:48
libplacebo version: v7.351.0 (v7.351.0-dirty)
FFmpeg version: N-120342-g3cd4fa9b8
FFmpeg library versions:
   libavcodec      62.8.100
   libavdevice     62.0.100
   libavfilter     11.3.100
   libavformat     62.1.103
   libavutil       60.6.100
   libswresample   6.0.100
   libswscale      9.0.100

Other Information

- Windows version: Win10 22H2
- GPU model, driver and version:
- Source of mpv: https://github.com/shinchiro/mpv-winbuild-cmake
- Latest known working version:
- Issue started after the following happened:

Reproduction Steps

• play any video with two external subtitles
  mpv any.mp4 --sub-files-append=1.srt --sub-files-append=2.srt --log-file=log.txt --pause
• run set sid 1 in console
• run set secondary-sid 2 in console
• run sub-reload 2 in console

Expected Behavior

there's no change in sid and secondary-sid

Actual Behavior

sid from 1 changed to 2 and secondary-sid from 2 changed to no

Log File

log.txt

Sample Files

two_external_subtitles.zip

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

• I tested with the latest mpv version to validate that the issue is not already fixed.
• 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.

Reproduce the issue with mpv using two external subtitle files, then run the listed sid, secondary-sid, and sub-reload commands while reviewing the attached log. Trace the subtitle reload handling related to these properties; done means sub-reload 2 leaves sid at 1 and secondary-sid at 2.