Trill lines

[Maurizio Tomasi]

I have a little problem with trill wavelines using lilypond 1.5.59.  I
want to have a trill line which is a bit above its default position.  If I
compile the following script (taken from input/test/trill.ly):

-----------------------------------------------------------------
\score {
  \context Staff \notes \relative c'' {
    \property Voice.TextSpanner \set #'type = #'trill
    \property Voice.TextSpanner \set #'edge-height = #'(4 . 4)
    \property Voice.TextSpanner \set #'edge-text =
        #'((line (music "scripts-trill") " ") . "")
    c\spanrequest \start "text" d e d \spanrequest \stop "text"
  }
}
-----------------------------------------------------------------

I get two vertical dashed lines that connect the waveline with the first
and last noteheads below the trill line.  Is there a way to get rid of
these lines?

Maurizio