non-printed text spanner

[James Bailey]

I'm curious as to why the text in this spanner isn't printed:
\include "deutsch.ly"
\version "2.12.3"

test = \relative c'' {
   \time 6/8
   c8 ges' f h,4( c8~   | %10
   c4 f8~ f4.) | %11
}

text = {
   \once \override TextSpanner #'(bound-details left text) = "poco rit."
   s4. s\startTextSpan  | %10
   s2 s8. s16\stopTextSpan \bar "||" %11
}

\score {
   \new Staff = treble <<
      \test
      \text
   >>
}