Taking screenshots may make subtitles corrupt #4325

mpv version and platform

mpv git-bba08e38ff (C) 2000-2017 mpv/MPlayer/mplayer2 projects
 built on Sun Apr 16 17:01:43 EEST 2017
ffmpeg library versions:
   libavutil       55.58.100
   libavcodec      57.89.100
   libavformat     57.71.100
   libswscale      4.6.100
   libavfilter     6.82.100
   libswresample   2.7.100
ffmpeg version: 3.3

Reproduction steps

Watch an anime with AlphaSubstation subtitles. Take a screenshot.

Expected behavior

Screenshot is made and subtitles are shown correctly afterwards.

Actual behavior

Goes from

to

The extra screenshots made later on with mpv still look correct, despite the incorrect rendering on the screen.

Log file

http://sprunge.us/jJUK

Sample files

This is reproducible with 15th episode of Little Witch Academia from Asenshi, though I have been able to reproduce the same behaviour in a multiple cases for at least 3 months now.

https://0x0.st/xj-.mkv is a piece that I cut out with ffmpeg which can reproduce it. Interestingly it does not reproduce without the included custom font streams.