scheme spanner in input/regression/scheme-text-spanner.ly not quote-proof

[Reinhold Kainhofer]

The text spanner implemented in scheme (which is also used as a basis
for David's measure counter engraver) seems to work fine in the regtest,
but apparently it is not quote-proof.

In particular, if you try call \addQuote on some music that contains
\schemeTextSpannerStart or \schemeTextSpannerEnd, then you get the
following warnings and the text spanner is not quoted:

scheme-text-spanner.ly:210:5: warning: Event class should be a list
  a4
     b\schemeTextSpannerStart c d |
scheme-text-spanner.ly:212:7: warning: Event class should be a list
  a4 b
       c\schemeTextSpannerEnd d |

So apparently the scheme way to add new event classes is not entirely
correct...
Sample file (regtest adapted to quote the music) is attached.

Any idea about the correct fix to this?

Thanks,
Reinhold

-- 
------------------------------------------------------------------
Reinhold Kainhofer, address@hidden, http://www.kainhofer.com
 * Financial & Actuarial Math., Vienna Univ. of Technology, Austria
 * http://www.fam.tuwien.ac.at/, DVR: 0005886
 * Edition Kainhofer, Music Publisher, http://www.edition-kainhofer.com

scheme-text-spanner.ly
Description: Text Data