DynamicText artificially extends bar size when within a StaffGroup

[Jean-Baptiste Mazon]

Hi,

I discovered this on my local 2.19.81, but it appears to be a regression
somewhere between 2.18.2 and 2.19.55 (compare http://lilybin.com/h2ixxn/1
and http://lilybin.com/h2ixxn/2)

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\version "2.18.0"

% The \tweak isn't necessary per-se, it just makes it more visible
dyn = \tweak DynamicText.self-alignment-X #LEFT
  #(make-dynamic-script (markup #:normal-text
    "dynamic text shouldn't push next bar to the right"))

% Occurs within a StaffGroup:
\score { \new StaffGroup { r r r e''\dyn e'' e'' e'' e'' e'' } }

% But not out of it:
\score { \new Staff      { r r r e''\dyn e'' e'' e'' e'' e'' } }
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

Cheers,
JBM