The buttons on the popover where stealing the focus from the text
view on click, causing the popover to be dismissed before the action
was taken. Fix this by making the buttons not take focus on click.
GtkWidget *item, *image;
item = gtk_button_new ();
+ gtk_button_set_focus_on_click (GTK_BUTTON (item), FALSE);
image = gtk_image_new_from_icon_name (icon_name, GTK_ICON_SIZE_MENU);
gtk_widget_show (image);
gtk_container_add (GTK_CONTAINER (item), image);