The issue is present in 3.0.0-beta1 and 3.x-dev, and does seem to be the same typo mentioned in the core issue you linked: https://github.com/ableplayer/ableplayer/issues/581#issuecomment-1648586370
I was using a remote video (YouTube), and haven't tried with a local video. It is affecting all caption preferences (background, text color, etc).
odlein → created an issue.