Same problem here. I've spend two day debugging what the hell is wrong with my web framework and today I noticed it isn't my framework which is broken. I'm running Twisted Web server on 8500 port at localhost and it's session system doesn't work because OmniWeb doesn't offer any cookies. There's temporary cookie assigned to domain localhost.local.

I've found a simple workaround for this. Edit /etc/hosts and put assing some domain name to 127.0.0.1.