Alignment of text mark is lost when an offset is applied

[Ed Gordijn]

Hi,

When I apply an offset to a text mark the alignment changes. The behaviour is
different for marks centered on the clef and marks centered on bar lines but
both are not correct (or not conform the IR). In the example below you should
expect a shift to the right for both marks.

I tested version 2.13.39 and 2.13.54.

See also: 
http://old.nabble.com/Alignment-of-text-mark-in-a-function-td31316227.html

Greetings, Ed

%\version "2.13.54" % identical behaviour in this version
\version "2.13.39"

\relative c'' {
    % Mark centered on the clef
    \mark \markup {\box "xxxx"}
    c1 c  \bar "||"
    % Mark centered on a bar line
    \mark \markup {\box "xxxx"}
    c1 c
    \break

    % Offset should move both marks to the right
    % Alignment on the clef is lost whem an offset is applied.
    \override Score.RehearsalMark #'X-offset = #2
    \mark \markup {\box "xxxx"}

    % Alignment on bar line changes to #LEFT
    % overriding self-alignment doens't change this
    % \override Score.RehearsalMark #'self-alignment-X = #CENTER

    c1 c  \bar "||"
    \mark \markup {\box "xxxx"}
    c1 c
  }

  \layout{
      indent = 0
      ragged-right = ##t

      \context {
          \Staff
          \remove "Time_signature_engraver" }
  }