gsf_output_stdio_new() does not touch filesystem

I'm writing a program which outputs a structured zip file. The original language is vala. Below is an extract of the generated c code.

  output = (GsfOutputStdio*) gsf_output_stdio_new (self->priv->_filename, &_inner_error_);
  if (_inner_error_ != NULL) {
   goto __catch2_g_error;
   goto __finally2;
  }
  _tmp1_ = (GsfOutfileZip*) gsf_outfile_zip_new ((GsfOutput*) output, &_inner_error_);
  if (_inner_error_ != NULL) {
   _g_object_unref0 (output);
   goto __catch2_g_error;
   goto __finally2;
  }
  self->outfile = (_tmp2_ = (GsfOutfile*) _tmp1_, _g_object_unref0 (self->outfile), _tmp2_);
...

  gsf_output_close ((GsfOutput*) self->outfile);

I have confirmed using gdb that this code is all executed. However, it fails to create a file on the filesystem or to put data into a file created in advance using touch. No error is generated and the output and outfile objects are not null.

ProblemType: Bug
Architecture: i386
Date: Sat Dec 19 17:46:31 2009
DistroRelease: Ubuntu 9.10
NonfreeKernelModules: nvidia
Package: libgsf-1-dev 1.14.15-1ubuntu1
ProcEnviron:
 LANG=en_NZ.UTF-8
 SHELL=/bin/bash
ProcVersionSignature: Ubuntu 2.6.31-14.48-generic
SourcePackage: libgsf
Uname: Linux 2.6.31-14-generic i686