http://bugs.debian.org/150467
The problem deals with user-defined chain names clashing with iptables module names. Basically, it's entirely possible to create a user-defined chain with the same name (case sensitive) as a target module, but the new chain cannot be used as a jump target. It is a packaging problem of sorts because an upgrade with new modules can suddenly conflict with existing user-defined chains. As always, don't shoot the messenger.
