annotate-spacing causing error

[Nick Payne]

Some sort of strange interaction here (I'm running 2.13.37 amd64 on 
Linux). Lilypond barfs on this:

%====================================
\version "2.13.37"

\header {
    title = "Title"
}

\paper {
    annotate-spacing = ##t
    system-system-spacing #'space = #3
}

\relative c'' {
    \repeat unfold 1024 { c4 }
}
%====================================

with the following error in the console log:

Parsing...
Interpreting music... 
[8][16][24][32][40][48][56][64][72][80][88][96][104][112][120][128][136][144][152][160][168][176][184][192][200][208][216][224][232][240][248][256]
Preprocessing graphical objects...
Finding the ideal number of pages...
Fitting music on 1 or 2 pages...
Drawing 
systems.../usr/local/lilypond/usr/share/lilypond/current/scm/stencil.scm:667:41: 
In procedure assoc in expression (assoc-get sym spacing-spec ...):
/usr/local/lilypond/usr/share/lilypond/current/scm/stencil.scm:667:41: 
Wrong type argument in position 2 (expecting association list): ((space 
. 3) . #<variable 7fc15c551c60 value: #0#>)

If I remove either one of the two settings in the paper block, then it 
builds without error. So either setting is valid on its own, but not if 
both are used together.

Nick