1.7.26 - unnecessary helper lines?

[Hans Forbrich]

Testing 1.7.26, every place in my score that has a 'flat' symbol gets
(what appear to be) additional helper lines - 2 above the flat symbol, 1
directly under and 2 below.  Occurs for all flat (eg ees and eeses) at
notes and in key signature, but not for any sharp or naturals.

Not sure whether I have an issue with my config or whether this is a
bug.  My test case, for which I have a .ps if needed, is

\version "1.7.24"
\paper { papersize = "letter" }
global=\notes {
        \time 2/4
        \key f \major
}

\score {

  <
     \context PianoStaff \notes <
        \context Staff = up % \autochange  Staff
        <
           \global
           \clef violin
           \context Voice = pa { a b c d e f ees }
        >
        \context Staff = down <
           \global
           \clef bass
           \context Voice = pc { a b c d e f ees }
        >
     >
  >
  \paper { }

}