i18n: label vs. clist title?

I have a <class>GtkCList</class> with <class>GtkLabel</class>
<child_name>CList:title</child_name>, two of them even (column
headings), one is <label>Property</label> and the other is
<label>Value</label>.  I also have two standalone
<class>GtkLabel</class>, one is <label>Value:</label>, the other is
<label>Property Name:</label>.  These all show up in the
<translatable_strings_file>:
gchar *s = N_("Property");
gchar *s = N_("Value");
gchar *s = N_("Property Name:");
gchar *s = N_("Value:");

and from there, in the app.po file:

#: bins-edit-gui-xlate-table:21
msgid "Property"
msgstr ""

#: bins-edit-gui-xlate-table:22
msgid "Value"
msgstr ""

#: bins-edit-gui-xlate-table:23
msgid "Property Name:"
msgstr ""

#: bins-edit-gui-xlate-table:24
msgid "Value:"
msgstr ""

and from there via msgmerge, they show up in the fr.po file:

#: bins-edit-gui-xlate-table:21
msgid "Property"
msgstr "Attribut"

#: bins-edit-gui-xlate-table:22
msgid "Value"
msgstr "Valeur"

#: bins-edit-gui-xlate-table:23
msgid "Property Name:"
msgstr "Nom de l'attribut"

#: bins-edit-gui-xlate-table:24
msgid "Value:"
msgstr "Valeur:"

They do even appear in the app.mo file:

Attribut^@Nom de l'attribut^@Valeur^@Valeur:^@

When I run the app, however, only the standalone labels (Nom de
l'attribut and Valeur:) get translated.  The labels in the CList (the
column headings) do not.  What am I missing, or is there a bug here?
This is my first real experience with gettext and translations (I'm
only doing a high-school-french level translation as an example so I
can verify that it all works...)