set-global-staff-size undoes define fonts

[David F.]

I can specify the font for my score to use with #(define fonts … ), but calling 
#(set-global-staff-size) undoes the font definition.

In the snippet below, Times New Roman will be used as the font for the whole 
document.  But if line 6 is uncommented, the font reverts to the default of New 
Century Schoolbook.  (These fonts are easily distinguished by the letter 
Q—hence the title.)

Any suggestion on how I can both set the font to TNR and set the staff size (in 
that order)?

=======
\version "2.19"

\paper {
    #(define fonts (make-pango-font-tree "Times New Roman" "" "" 1))
}
% #(set-global-staff-size 20)

\header {
    title = "QQQ"
}

\relative c' {
  c c c c
}
=======

Thanks,
David