As noted above this: %$self = %$newSelf; is really suspicious. (Update: actually, it is just unnecissary.)

But wait! There's more!

The default serializer of CGI::Session cannot thaw frozen objects properly. You have to use FreezeThaw as the serializer.

This is documented in CGI::Session::Serialize::Default but I never even knew it existed that one until I started looking for it.

More information: http://author.handalak.com/archives/112003/000364

Hope this helps.
Joost.