Overlapping rests in multiple voices

Hi,
I'm new to Musescore and to software notation in general. I'm using v1.2 on Mountain Lion.
I'm writing a piece for guitar on a single stave (lead sheet.mscx) with multiple voices.
When I try to notate two rests of different durations in two different voices, the rests overlap rather than stack above and below one another like the notes do. No problem with the notes, following the instructions in the handbook under 'voices', just can't seem to get the rests to show.
Anything I can do to show both rests?
Thanks,
Steve