Hi Peter,
> The following MWE shows that the full bar rests are not shifted as I would
> have expected in the parallel voices. Bars 5 and 6 print the rests at
> different heights. Have I missed a property somewhere?
Well, rests are Rest, and full-bar rests are MultiMeasureRest… ;)
> Alternatively, can some one help me place the markup at the beginning of the
> bar?
Why use a markup? Wouldn’t it be [semantically] correct/superior as a mark (or
tempo)? e.g.
\tweak self-alignment-X #LEFT \mark \markup \italic "Ritard."
Hope that helps!
Kieren.