10.5_vanilla.catalog

I have InstaDMG (rev 339) and I noticed the "10.5_vanilla.catalog" file has the folowing: Mac OS X 10.5.8 Combo Update QuickTime 7.6.6 for Leopard AirPort Utility 5.3.2 Leopard AirPort Utility Software Update 5.4.2 AirPort Base Station Update 2010-001 5.5.1 Security Update 2010-004 Front Row Update 2.1.7 Java For MacOS X 10.5 Update 5 Remote Desktop Client 3.3.2 Java For MacOS X 10.5 Update 7 Security Update 2010-005 My question is this: Why do we need the "Security Update 2010-004" if the "Security Update 2010-005" supercedes it? BTW: I have found that if I remove the "Security Update 2010-004" and only install the "Security Update 2010-005", "Software Update" is fine with it. Why do we have both of these entries? Is there a reason for it?