Rehearsal mark alignment change from 2.16 to 2.17

[Jim Long]

I did a build of 2.17.26 on FreeBSD today to try things out, and
quickly found one change I wanted to inquire about.

Given this code:

\score {
  \new Staff \relative c' {
    \override RehearsalMark #'break-align-symbols = #'(clef bar)
    \mark \default
    c1
    \mark \default
    c1
  }
}

2.16.2 centers each mark over its alignment symbol (the clef and
the barline, respectively).

But in 2.17.26, the first mark is left-aligned with the
centerline of the clef, while the second mark is center-aligned
over the barline.

Is this intentional, or a mild bug?

Thanks!

Jim