Thanks for your message.
The problem is, that WordPress does not send any feedback to the user if the comment is marked as spam (due to blacklisted words). My plugin just "ajaxifies" the default WordPress comment workflow, i.e. if WordPress does not send any feedback to the user without my plugin, there is also no feedback when using the AJAX way.
What you can do is write a little customization that shows an appropriate message to the user in the default WordPress comment feeedback workflow (just like the "ERROR: please fill the required fields (name, email)." message) and my plugin will show exactly this message in a popup.
Hope this helps...