In rich text is possible that in a pair of chars that from a ligature the first char in the pair is the last char a text span and second char the first on following text span. When this happens the ligature is broken. But if both text spans have the same font it should be possible to preserve it.

We had this working on T2k for some cases but the correct fix should require our text itemizer to tell part contextual ligatures from clusters which we never implemented..