Staff change at beginning of score

[Yuval Harel]

It seems staff changes don't work at the beginning of a score. In this  
example, the {a} is incorrectly produced in the right-hand staff:

\version "2.4.2"

\score {
    \context PianoStaff=PS <<
        \context Staff=RH {
            \change Staff=LH a
        }
        \context Staff=LH {
            \clef bass
            c4
        }
    >>
}


Adding notes before the {a} prevents this problem.

Outside the main voice, the change works, but \stemUp (or \voiceOne) has  
no effect:

\version "2.4.2"

\score {
    \context PianoStaff=PS <<
        \context Staff=RH {
            \context Voice="1" {\change Staff=LH \stemUp a}
        }
        \context Staff=LH {
            \clef bass
            \stemDown c
        }
    >>
}

Thanks,
        Yuval