Hi Bob,
even though I conceived the code, I can unfortunately neither reproduce nor explain the error. In case you like to dig a bit deeper, the offending function can be found in 'manual/manual.gosh'. The variable 'chapter_tag' contains the string for the markup of a chapter. It is defined at line 548 of the 'gosh' script.
To remove the road block for you reading the documentation, I built and uploaded the current version to here:
http://genode.org/files/e01096b9ffe3f416157f6ec46c467725/manual-2015-01-23.p...
Cheers Norman