So the worst thing that can happen on a contact for is to tell the sender their message was sent, and not send it.
I configured the form accidentally to do this by enabling text processing for the contact form, but not checking "Text analysis" for spam or profanity or checking any fields to analyse. I don't remember if these were the defaults, or I unchecked them.
Anyways, in this state, I got the following warnings and a false positive message:
warning: Invalid argument supplied for foreach() in /var/aegir/hostmaster-6.x-1.6/sites/all/modules/contrib/mollom/mollom.module on line 1059.
warning: implode(): Invalid arguments passed in /var/aegir/hostmaster-6.x-1.6/sites/all/modules/contrib/mollom/mollom.module on line 1707.
Your message has been sent.
Either the config form should prevent this configuration, or the module should not throw warnings and a false message.