Multiple rest and system break

[Menu Jacques]

Hello folks,

This beats me : in the following snippet, why is there a break after ‘R1*2’ ? 
There seems to be plenty of room to put everything on a single line…?

Thanks for your help!

JM


%%%%%%%%%%%%%%%%%
\version "2.19"

P_POne_Staff_One_Voice_One = \relative {
  \compressMMRests

  R1*2 |
  R1   |
  r2 r4 r8 r16 r32 r64 r128 r128 |
  \bar "|."
}

\score {
  <<
      \new Staff <<
        \context Voice = "P_POne_Staff_One_Voice_One" <<
          \P_POne_Staff_One_Voice_One
        >>
      >>
  >>

  \layout {
  }
}
%%%%%%%%%%%%%%%%%