staffname not shown

[Stefan Thomas]

Dear community,
the second staffname in the below snippet is not displayed. I don't unterstand, why:
\version "2.12.2"
notiert = \relative c'' {
\grace c8 b2 c4 r 
}
ausfuehr = \relative c'' { 

  c4(->\> b\!) c4 r4 \bar"||"
}
\score { 
 <<
   \new Staff  { \set Staff.instrumentName = "Notation" \notiert }
 \new Staff { \set Staff.instrumentName = "Ausführung" \ausfuehr }

>>
}