--To reproduce--
start application and login
create one domain and one host
from the Console hierarchy view, select host, and invoke the attribute editor
    within the popup menu

notice the error message in the SyMON-Console Messages window:

info Jan 14 10:05:57 console-runner: Message buffer enabled.
stderr Jan 14 10:18:41 AWT-EventQueue-0: Received a mouse event from a non-showi
ng Component com.sun.java.swing.JMenuItem[,1,3,151x17,layout=com.sun.java.swing.
OverlayLayout]

** NOTE **
This happens on the initial login and on the first initial operation


--System Info--
all components are installed, configured, and running on this system

SunOS cujo 5.6 Generic sun4u sparc SUNW,Ultra-1

                          Solaris 2.6 s297_37cshwp SPARC
           Copyright 1996 Sun Microsystems, Inc. All Rights Reserved.
                      Manufactured in the USA 18 July 1997