It isn't really interesting to know why it doesn't work with the legacy subtitle engine as that is no longer supported by BS.Player team. So even if it is a bug, it will not be repaired anymore. At present BS.Player team only supports the new subtitle parser/renderer and using that seems to have solved your problems.
With respect to the other problem: if none of the posts in the threads to which I placed direct links (e.g.
this post) helps you, I'm afraid I personally don't know how to help you on this.