This is with atk 1.26.0 and gtk-doc 1.11 on Mandriva Cooker.

gtk-doc: Running scanner atk-scan
touch scan-build.stamp
gtk-doc: Rebuilding template files
cd . && gtkdoc-mktmpl --module=atk
./atk-unused.txt:1: warning: 9 unused declarations.They should be added to atk-sections.txt in the appropriate place.
touch tmpl-build.stamp
gtk-doc: Building XML
cd . && \
        gtkdoc-mkdb --module=atk --source-dir=../atk --output-format=xml --expand-content-files="" --main-sgml-file=atk-docs.sgml
../atk/atkrelation.c:344: warning: Free-form return value description in atk_relation_remove_target. Use `Returns:' to avoid ambiguities.
../atk/atkhyperlink.c:366: warning: multi-line since docs found
../atk/atkhyperlinkimpl.c:52: warning: Free-form return value description in atk_hyperlink_impl_get_hyperlink. Use `Returns:' to avoid ambiguities.
../atk/atkimage.c:198: warning: Free-form return value description in atk_image_get_image_locale. Use `Returns:' to avoid ambiguities.
../atk/atkobject.c:876: warning: atk_object_get_layer is deprecated in the inline comments, but no deprecation guards were found around the declaration. (See the --deprecated-guards option for gtkdoc-scan.)
../atk/atkobject.c:904: warning: atk_object_get_mdi_zorder is deprecated in the inline comments, but no deprecation guards were found around the declaration. (See the --deprecated-guards option for gtkdoc-scan.)
../atk/atkobject.c:1580: warning: Free-form return value description in atk_object_add_relationship. Use `Returns:' to avoid ambiguities.
../atk/atkobject.c:1609: warning: Free-form return value description in atk_object_remove_relationship. Use `Returns:' to avoid ambiguities.
../atk/atkaction.c:103: warning: Free-form return value description in atk_action_get_description. Use `Returns:' to avoid ambiguities.
../atk/atkaction.c:142: warning: Free-form return value description in atk_action_get_name. Use `Returns:' to avoid ambiguities.
../atk/atkaction.c:168: warning: Free-form return value description in atk_action_get_localized_name. Use `Returns:' to avoid ambiguities.
../atk/atkaction.c:205: warning: Free-form return value description in atk_action_get_keybinding. Use `Returns:' to avoid ambiguities.
../atk/atkstreamablecontent.c:75: warning: Free-form return value description in atk_streamable_content_get_mime_type. Use `Returns:' to avoid ambiguities.
../atk/atkobject.h:339: warning: Documentation in template ./tmpl/atkobject.sgml:298 for AtkPropertyValues being overridden by inline comments.
../atk/atkstate.h:123: warning: Value described in source code comment block but does not exist. ENUM: AtkStateType Value: note.
98% symbol docs coverage (341 symbols documented, 0 symbols incomplete, 6 not documented)
See atk-undocumented.txt for a list of missing docs.
The doc coverage percentage doesn't include intro sections.
cmp: ungültiger --ignore-initial-Wert »./xml/api-index-ATK«.
cmp: »cmp --help« gibt Ihnen mehr Informationen.
Error running 'cmp ./xml/api-index-ATK 1.9.xml ./xml/api-index-ATK 1.9.new' at /usr/share/gtk-doc/data/gtkdoc-common.pl line 60.