Here is part of the code to manage the statusbar :

     if (flash_message)
-      g_timeout_add (15000, gm_statusbar_clear_msg_cb,
-                    GINT_TO_POINTER (msg_id));
+    {
+#if GTK_CHECK_VERSION(2, 14, 0)
+      g_timeout_add_seconds (15, gm_statusbar_clear_msg_cb, 
+                      GINT_TO_POINTER (msg_id));
+#else
+      g_timeout_add (15000, gm_statusbar_clear_msg_cb, 
+                      GINT_TO_POINTER (msg_id));
+#endif
+    }

Here we have a bug : we set a timer to clear the flash bar in 15s...
what happens if :
time: we display a message
time+14.999s: we display another, very important message
time+15s: we clear the status bar
?

The user won't get the message!

Solution :
(1) store the result of g_timeout_add ;
(2) when a new message arrives, cancel the timeout if there is one, and set one anew ;
(3) when clearing, clear the stored result too to avoid cancelling a non-existing timeout.

This one's very easy : gnome-love!