hey john,
this is actually the default behaviour of easydisucss. think of it this way: when a user posts a question / reply without any attachment it gets processed (accepted). therefore when "only" the attachment fails easydiscuss is treating the post as if this attachment wouldn't exist and therefore still allows the posting of the text itself

however if you'd think that having an option to block the whole post in this case would be a good enhancement feel free to post this idea to our voices section at http://stackideas.com/voices

this is the place we're monitoring when it comes to feature implementation for upcoming releases. hope that helps and have a nice day