GtkPlug, and browser plugins

Anyone familiar with GtkPlug? I’m having issues with the PackageKit XEmbed browser plugin — unless I set the sizes for the widgets using gtk_widget_set_size_request, or set the widgets to expand to all the space, I get widgets with close to zero width and height:

The line across the widget is meant to be a GtkButton! Ideas welcome, and experts rewarded by beer! If anyone has examples of how to do a browser plugin with GTK controls, that would be great too. Thanks!