Two rhythms same stave

Hello,
I'm trying to transpose a 4 part brass quartet for grand piano, and am trying to put two different rhythms onto the treble clef. It works with two different pitches if they're the same rhythm, but the new entry overrides the old one if they're different rhythms. Am I doing something wrong or is this just not possible? I'm using musescore 2 with revision:f51dc11
Thanks!