how to make more than one textspanner at once

[Stefan Thomas]

Dear community,
I try to get two textspanners at the same time.
It works fine, but: I can't see the stringendo-Text!
What could be the reason?
Here is my snippet:

%%%%%%%% BEGIN %%%%%%%%%%%
\version "2.12.2"
\layout
{
        \context
        {
                \type "Engraver_group"
                \consists "Text_spanner_engraver"
                \consists "Axis_group_engraver"
                \name "ConTextSpan"
                \override VerticalAxisGroup #'minimum-Y-extent = #'(1 . 3)
        }
        \context { \Score \accepts ConTextSpan }
        \context { \Voice \remove "Text_spanner_engraver" }
}


stringendo = { \textSpannerUp \override ConTextSpan.TextSpanner #'style = #'line \override ConTextSpan.TextSpanner #'(bound- details left text) = "Stringendo" } 
% why I don't see the stringendo?

global = {
  \time 2/4 s2
  \stringendo
  c2 \startTextSpan c \stopTextSpan 
  s2
}
music = \relative c' {
 \new Voice \with { \consists Text_spanner_engraver } 
 { \textSpannerDown \override TextSpanner #'(bound-details left text) ="hello" c4 \startTextSpan  d e f g2 e \stopTextSpan } 
}


\score {
  <<
    \new ConTextSpan \global
    \new Staff \music
  >>
}


%%%%%%%%%%%%%% END %%%%%%%%%%%%%%