`blend-subtitles=yes` breaks subtitles when using `video-crop`

Important Information

Provide following Information:

• mpv version: master
• Platform and Version: Arch Linux
• Source of the mpv binary: own build
• If known which version of mpv introduced the problem: f3f1a79fe3ad9bdae344559ec5802c184af41112; i.e. addition of video-crop
• GPU model, driver and version: N/A
• Possible screenshot or video of visual glitches: N/A

Reproduction steps/Actual behaviour

Download the example video files.

• 816p-native.mkv - 1920x816 video
• 1080p-crop.mkv - 1920x816 video (cropped from 1920x1080 using Matroska PixelCrop properties)
• 1080p-crophalf.mkv - 1920x948 (cropped from 1920x1080 using Matroska PixelCrop properties)
• 1080p-native.mkv - 1920x1080 (no crop applied, can apply yourself with video-crop, will behave the same)

Inconsistent SRT font size

1. Set blend-subtitles=yes
2. Play 816p-native.mkv video
3. Play 1080p-crop.mkv video, font size is smaller than 816p-native.mkv

Cropped ASS text

1. Set blend-subtitles=yes and sid=2
2. Play 816p-native.mkv video, text appears correctly
3. Play 1080p-crop.mkv video, text is not visible
4. Play 1080p-crophalf.mkv video, text is half cropped and not blended with video

Expected behaviour

Inconsistent SRT font size

816p-native.mkv and 1080p-crop.mkv should have the same font size.

Cropped ASS text

816p-native.mkv, 1080p-crop.mkv should look the same.

1080p-crop.mkv with blend-subtitles=no looks identically to 816p-native.mkv with blend-subtitles=yes

(not sure how 1080p-crophalf.mkv should look like regardless of the blend-subtitles)

Log file

Zipped logs of all test runs

Sample files

(UPDATED)
Zipped example Matroska files

[Script Info]
ScriptType: v4.00+
PlayResX: 1920
LayoutResX: 1920
LayoutResY: 816
PlayResY: 816
ScaledBorderAndShadow: yes
YCbCr Matrix: TV.709

[V4+ Styles]
Format: Name, Fontname, Fontsize, PrimaryColour, SecondaryColour, OutlineColour, BackColour, Bold, Italic, Underline, StrikeOut, ScaleX, ScaleY, Spacing, Angle, BorderStyle, Outline, Shadow, Alignment, MarginL, MarginR, MarginV, Encoding
Style: Default,Arial,70,&Hffffff,&Hffffff,&H0,&H0,0,0,0,0,100,100,0,0,1,1,0,2,10,10,10,1

[Events]
Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text
Dialogue: 0,0:00:00.00,0:00:10.00,Default,,0,0,0,,Consistency goes brrrrrr

[Script Info]
ScriptType: v4.00+
PlayResX: 1920
LayoutResX: 1920
LayoutResY: 1080
PlayResY: 1080
ScaledBorderAndShadow: yes
YCbCr Matrix: TV.709

[V4+ Styles]
Format: Name, Fontname, Fontsize, PrimaryColour, SecondaryColour, OutlineColour, BackColour, Bold, Italic, Underline, StrikeOut, ScaleX, ScaleY, Spacing, Angle, BorderStyle, Outline, Shadow, Alignment, MarginL, MarginR, MarginV, Encoding
Style: Default,Arial,70,&Hffffff,&Hffffff,&H0,&H0,0,0,0,0,100,100,0,0,1,1,0,2,10,10,10,1

[Events]
Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text
Dialogue: 0,0:00:00.00,0:00:10.00,Default,,0,0,0,,Consistency goes brrrrrr

Screenshots

Start by reproducing the issue with the sample files in examples-v2.zip, comparing blend-subtitles=yes and no with video-crop applied. Trace the entry points for the blend-subtitles and video-crop options, then verify that cropped and native videos produce consistent SRT sizing and correctly positioned ASS subtitles.