If you use Red October HQ, don't make any changes to it, just for testing.
OK I will leave my MadVR on 127.0.0.1
Made same test for ASS/SSA 4.0+
Same things are observed:
1. when MC is paused in ROHQ ... MC keeps redrawing subtitles (smaller versions) ... see attached MC screen shot (this does not happen in ROstd]
2. first sub to appear looks correct size and position ... as new one start to appear ... positioning and font size seem to scale incorrectly (sub were made for 1280x720 but run on 1920x1080 video) ... its hard to tell wheter [MarginL] [MarginR] [MarginV] is implemented
3. as each sub start to disappear ... remaining sub on screen get redrawn in different positions and font sizes
4. [OutlineColor] [BackColour] [BorderStyle] [Outline] [Shadow] gets ignored ... instead MC always draws outline and shadow in black (this causes the problem when font color is black as can be seen from screenshots)
5. [Bold] [Italic] are ignored
All additional features of ASS for [Style] are ignored:
6. [Underline] [StrikeOut] [ScaleX] [ScaleY] [Spacing] [Angle]
7. Alpha values in [PrimaryColour] [SecondaryColour] [OutlineColor] [BackColour]
On positive side MC handles changes in specification for [Alignment] correctly. On additional negative side, ROstd quality of rendering is nowhere near ROHQ
Attachment include zipped subtitle file (use it together with mkv attached in first post ... don't forget to rename them to same name)
I will not test override codes at the moment because their correct function largely depend on correct implementation of styles (unless you tell me otherwise)