I'm not sure what kind of anti-spam filter you are using but I have to tell you, few things make me want to go do something else for a week like losing a detailed reply on submit.
WPMU, we REALLY REALLY REALLY need to error trap this stuff. When I hit "Submit" and end up back on the post index, then the back button returns me to a blank form, it makes me want to light a kitten bonfire.
Please fix this behavior. It's incredibly frustrating to deal with.