Namespace-ill-formed output from Genx

It looks like Genx tries hard to ensure its output is 
namespace-well-formed, but if I write:

   #include "genx.h"
   int main(int argc, char * argv[])
   {
     genxWriter w = genxNew(NULL, NULL, NULL);
     genxStartDocFile(w, stdout);
     genxStartElementLiteral(w, NULL, ":");
     genxEndElement(w);
     genxEndDocument(w);
   }

then the output is <:></:> which is not good. (In particular, 
checkNCName seems to allow the first character (but no other) to be 
':'). Would I be right in thinking this is a bug?

-- 
Philip Taylor
pjt47@cam.ac.uk