BarNumber outside-staff-priority not honoured?

[Trevor Daniels]

The outside-staff-priority of BarNumber is set by default to
100, the lowest of all outside-staff objects, yet it appears
in 2.1.34 to be placed further from the staff than
DynamicText (250), DynamicLineSpanner (250), and
OttavaBracket(400).  Here is an illustration of an extreme
situation, followed by a minimal example with DynamicText
alone.

% Illustrative example
\version "2.11.34"
\relative c' {
\override Score.BarNumber #'break-visibility = ##(#t #t #t)
\override TextSpanner #'bound-details #'left #'text
          = \markup { \small \bold Slower }
\dynamicUp
  #(set-octavation 1)
  c \startTextSpan c\pp c\< \tempo 4 = 72
  c^Text \mark \default |
  c c c\ff c \stopTextSpan \mark \default |
  #(set-octavation 0)
  c c c c
}

% Minimal example
\version "2.11.34"
\relative c' {
\override Score.BarNumber #'break-visibility = ##(#t #t #t)
\dynamicUp
  c c c c |
  c\ffff c c c |
}

Trevor D