printing page numbers affects the number of pages?

[Vincent]

The following example takes 1 page if page numbers are printed, and
2 pages if they aren't (comment the two statements in \paper). 

Is this a bug? 

I think that the result should be the same with or without page 
numbers, but even if you don't agree with this, then shouldn't happen 
just the opposite? (if page numbers take score space --> chances are 
that the score can take more pages, not less)

Thanks,
Vincent

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\version "2.9.26"

\paper
{
  print-page-number = ##t
  print-first-page-number = ##t
}

\relative c'
{
  \time 4/4
 
 \repeat unfold 121
 {
  a' b c d
 }
}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%