Priorities are meaningless, calibre development is done by volunteers, which means that tickets get fixed if a calibre developer feels like fixing them.
I personally care very, very little for RTF (never use it). It is a very poorly designed format, so fixing bugs in it is difficult. As a result, RTF Input/RTF output related bugs tend to languish.
What's needed is a developer that actually uses RTF, unfortunately, no such beast seems to exist
