instrumentCueName prints twice

[James Worlton]

> I'm not top posting.

Hello,

The following code produces the instrumentCueName twice:

\version "2.13.38"
\addInstrumentDefinition #"two"
  #`((instrumentTransposition . ,(ly:make-pitch -1 0 0))
     (clefGlyph . "clefs.G")
     (clefOctavation . 0)
     (middleCPosition . -6)
     (clefPosition . -2)
     (instrumentCueName . ,(markup "Instr. Two")))

notes = \relative c' { c1 }
\score { 
    \new Staff = "one" { 
        \set Staff.instrumentName = "One "
        \notes
        \instrumentSwitch "two"
        \notes
    }           
}

However, if the \notes variable is removed and the notes are added directly into
the \score block, the duplication does not happen:

\version "2.13.38"
\addInstrumentDefinition #"two"
  #`((instrumentTransposition . ,(ly:make-pitch -1 0 0))
     (clefGlyph . "clefs.G")
     (clefOctavation . 0)
     (middleCPosition . -6)
     (clefPosition . -2)
     (instrumentCueName . ,(markup "Instr. Two")))

\score { 
    \new Staff = "one" { 
        \set Staff.instrumentName = "One "
        c'1
        \instrumentSwitch "two"
        c'1
    }           
}