2.17 example for changing entire document fonts swells noteheads and other elements

[Nick Payne]

If I use the define fonts example in the documentation at 
http://lilypond.org/doc/v2.17/Documentation/notation/fonts#entire-document-fonts 
to change the document fonts, the noteheads swell so that they no longer 
fit between the staff lines. Have a look at the PDF output for the 
example below at magnification. The noteheads overlap the staff lines. 
Other notational elements are affected as well - the loop of the treble 
clef no longer sits on the bottom staff line but goes below it, and the 
time signature no longer fits between staff lines. Without the define 
fonts in the paper block, all these elements are the correct size. I 
tried a few different fonts for the serif, sans, and monospaced 
typefaces, and the behaviour was the same for all. If I use the example 
from the 2.16 docs for changing document fonts, i.e.

\paper  {
  myStaffSize = #20
  #(define fonts
    (make-pango-font-tree "Times New Roman"
      "Nimbus Sans"
      "Luxi Mono"
      (/ myStaffSize 20)))
}

then the problem doesn't happen.

%===================
\version "2.17.10"

\paper {
  #(define fonts
    (make-pango-font-tree "Times New Roman"
      "Nimbus Sans"
      "Luxi Mono"
      (/ (* staff-height pt) 2)))
}

\relative c'{
    c d e f g a b c
}
%===================