different sizes for instrument names (Staff vs. PianoStaff)

[Marc Hohl]

Hello,

while working with lilypond I discovered that changes of the font size are
treated differently between Staff and PianoStaff.

Consider the following snippet:

\version "2.13.4"

stuff = \relative c {
 c4 d e f
 g a b c
}

\score {
 <<
   \new Staff = "Staff" \with { \override StaffSymbol #'staff-space = #2/3
                                fontSize = #(magnification->font-size 2/3)
                                instrumentName = #"Staff" }
   { \clef "treble"  \stuff }
   \new PianoStaff = "PianoStaff" \with { \override StaffSymbol 
#'staff-space = #2/3
                                          fontSize = 
#(magnification->font-size 2/3)
                                          instrumentName = #"PianoStaff" }
   <<
     \new Voice = "RH" { \clef "treble" \stuff }
     \new Voice = "LH" { \clef "bass" \stuff }
   >>
 >>
}

The "Staff" is scaled properly, whereas "PianoStaff" is not. I didn't 
find anything in the bug tracker,
but this seemed to be not the desired behavior.

Marc