Dynamics attached to spacers sometimes aligned incorrectly

[Greg]

> I'm not top posting.

This may be related to issue 3299 but I don't have the technical knowledge
to confirm this.

\version "2.18.2"

\score {
  <<
    \new Staff \relative g' {
      << g1 s1\sfz^"1" >> % sfz attached to spacer too far left
      \revert Script.self-alignment-X
      << g1 s1\sfz^"2" >> % correct position after revert
    }
    \new Staff \relative g' {
      << g1\sfz^"3" s1 >> % sfz correct when attached to note instead
      << g1 s1\sfz^"4" >> % sfz too far left as in no. 1
      g1\sfz^"5" % sfz correct when no spacer involved
      << g1 s1\sfz^"6" >> % sfz attached to spacer now correct
    }
  >>
}