problem wish TextSpanner dash-fraction

[Allan Spagnol Comar]

Hi, I am trying to use dash-fraction as 1.0 on my sheet, but when I
pass 1.0 the lilypond return error.... when I pass 0.9 it return
success....

I am attaching my .ly is :
\version "2.8.0"

\score
{
        \context Voice
        {
                \textSpannerUp
                \override TextSpanner #'edge-text = #'("C1" . "")
                \override TextSpanner #'dash-fraction = #1

                \relative c'
                {
                        f
                        \startTextSpan
                        a c
                        \stopTextSpan
                }
        }
}


 anyone knows what is wrong ?
--
An application asked:
"Requeires Windows 9x, NT4 or better",
so I´ve installed Linux