Instrument name in top line

[Helge Kruse]

When you add the "instrument" to the header block, it is printed below 
the title at the first page. It is also printed in each top line of 
subsequent pages.

But when you start a new bookpart the instrument name is printed on the 
first page too. This looks a bit ugly. How can I avoid this duplication? 
I would like to skip the instrument name in the top line at the first 
page of the bookpart.

Helge

\version "2.15.38"

melody = \relative c'' { \repeat unfold 100 { c4 d e f g f e d } }
\header { title="My Song" }
\book {
  \bookpart {
    \header { instrument = "Flute" }
    \new Staff { \melody }
  }
  \bookpart {
    \header { instrument = "Oboe" }
    \new Staff { \melody }
  }
}