Good idea with the work around! I've generally avoided the NWF.FormFiller.XXXX methodology because I'm unsure of what they do and I've been implementing my own buttons as well. Though that function seems to be fairly straight forward .
Sorry I didn't see your question sooner, I was quite busy this past week. Another option to consider for the future is to use jQuery and assign the class on form load. It's what I did to bypass the cancel button bug.