Piano Roll Doesn't Display Some Notes or Places Them in Wrong Octaves

The Piano Roll Editor in Musescore 3 is very useful and easy to read! I've experienced problems, though, when I open a MIDI piano file. Even though all of the notes load successfully in the main notation window, some of the notes are absent from the Roll Editor, or it displays some notes with the correct letter name, but in the wrong octave, e.g. the Piano Roll shows a note as "C4", when in the notation window (and in reality) it's a "C3". Almost all of the notes display perfectly in the Piano Roll, so the missing or improperly placed notes in the Piano Roll are the rare exception. I went back and opened the same MIDI file in Musescore 2, and it had the same problems with the same notes. Am I doing something wrong, or could this be a bug? Many thanks in advance for any help.