Hi a small suggestion
When your in the sub caps Edit master Captions list you can't play the timeline.
That for me it is a problem because you can't hear if the caption that you wrote was good or just to check if it's correct.
so my suggestion is to make it possible to play while the sub-cap is on and furthermore if there was an outline or a different color on the box that he is on.
I hope this was helpful and this of course is Just a suggestion.
best regards
Amir S