Does this work?

diff --git a/src/empathy-chat-window.c b/src/empathy-chat-window.c
index 801cf57..08a79d4 100644
--- a/src/empathy-chat-window.c
+++ b/src/empathy-chat-window.c
@@ -2068,8 +2068,9 @@ empathy_chat_window_add_chat (EmpathyChatWindow *window,
        gtk_notebook_append_page_menu (GTK_NOTEBOOK (priv->notebook), child, label, popup_label);
        gtk_notebook_set_tab_reorderable (GTK_NOTEBOOK (priv->notebook), child, TRUE);
        gtk_notebook_set_tab_detachable (GTK_NOTEBOOK (priv->notebook), child, TRUE);
-       gtk_notebook_set_tab_label_packing (GTK_NOTEBOOK (priv->notebook), child,
-                                           TRUE, TRUE, GTK_PACK_START);
+       gtk_container_child_set_property ( GTK_CONTAINER (priv->notebook), child, (gchar*) "tab-expand" , (GValue*) TRUE);
+
+       gtk_container_child_set_property ( GTK_CONTAINER (priv->notebook), child, (gchar*) "tab-fill" , (GValue*) TRUE);
 
        DEBUG ("Chat added (%d references)", G_OBJECT (chat)->ref_count);
 }

Nope it doesn't... sorry about that patch
R.

Created attachment 152441 [details] [review]
modifies tab-expand and tab-fill properties of child in chat-window

Thanks for your patch Reimundo. I fixed some minor still issues and merged it to master.

This problem has been fixed in the development version. The fix will be available in the next major software release. Thank you for your bug report.