Drum notation help

I'm hoping someone can help. I've got a MusicXML file exported from Logic for a drum part that I need to get into an existing score. However, when I copy the drum part from the XML, Musescore pastes all the notes onto the top line in the staff. The same thing happens when I assign the "large drum set" instrument the XML file. It also happens if I start from a MIDI file (as opposed to XML). Has anyone encountered this? Or does anyone have a process for getting MIDI drum parts into MuseScore?