Can I force a staff to continue for a new key signature?

[Peter Toye]

I want to do something slightly unusual: at the end of a score I want a new key signature. (I'm extracting bits and don't want the next bar, but do want the key change).

I tried this but the key change is printed without the staff lines.

\version "2.19.52"

\language "english"

\score {
  \new Staff {
    \key c \major
    c''1 1 1 1
    \bar "||"
    \break
    \key a \major
    %  a'1 1 1 1
  }
}

If I uncomment the last text line I get the staff lines back. Is there any way of doing this without printing the nest line?
 
Regards,

Peter
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www.ptoye.com