Are you seeing this with a font that used to look fine and didn't show the aliasing issue? If so then see if perhaps enabling the 1:2:1 deflicker option, which is located at the top of the filter controls might be the answer. How does it look when you view it on the computer screen as opposed to the Kona controlled monitor? How does the final render look? Are you viewing at 100 percent? At zooms higher than 100 percent, the text will have the aliased appearance that you are seeing.
Would it be possible for you to send me a screenshot so that I can see this as I cannot reproduce the problem on my system. And can you please set the view to 100 percent for the screenshot? You can send that to me at firstname.lastname@example.org.