I've been trying to work with MIDI and Sibelius for a while now and have reached the opinion that Sibelius does very few things well if any import or capture method is used. SOME MXML files go in OK, but MIDI very seldom does unless the MIDI has been carefully created with instruments named/located in the STANDARD positions. But just taking an acoustic piano from my Motif XS-8 for example is a mess. It doesn't split at C4 and yet much less expensive programs like "Notation Composer" do a great job of splitting a piano track and correctly attributing chords if you want them. However, when you output from Notation Composer to XML and then bring the XML into Sibelius, there are usually a ton of errors (alleged) by the Sibelius import.
The only way I've been able to get consistent results from MIDI to Sibelius is to either capture the MIDI with ProTools and then edit the score in PT and then save as Sibelius.