Subtitles are out-of-sync with the video when mpv open a BDMV video and external subtitles

Important Information

Provide following Information:

• mpv version: 0.35.0
• Windows Version: Windows 10 22H2
• Source of the mpv binary: Shinchiro mpv-x86_64-20230108-git-c8a9000
• If known which version of mpv introduced the problem: Unknown
• Possible screenshot or video of visual glitches: It's an subtitle problem.

Reproduction steps

1.Open a BDMV video.
2.Drag in a ASS subtitle.
3.Use the right arrow keys to jump 5 second backward for several times

Expected behavior

The subtitle can be synchronised with the video.

Actual behavior

The subtitle is a few seconds faster than the video.
But if I drag the video progress bar directly forward or backward, the previously out-of-sync subtitles get back in sync with the video.
This problem does not occur with other types of video files or built-in subtitles, nor does it occur when using KikoPlay, which is also mpv-based, to play BDMV and drag in subtitles.

Log file

mpv.log

Reproduce the issue with mpv 0.35.0 on Windows using a BDMV video and an external ASS subtitle, following the listed seek steps. Start by reviewing the attached mpv.log and the playback and subtitle-seeking paths; done means repeated 5-second seeks keep the external subtitle synchronized, as direct progress-bar seeks already do.