However it appears to be a stylesheet issue - When I switched to the default style, I was able to register without issue. I'd go back to Audentico and get them to fix it.
And Please... PLEase...PLEASE.... @turtile , DON'T do your custom edits on the default UIX style... make a child style and do the edits there and make that your default. The first time you go and upgrade your UIX, all the customizations you have made are going to get blown away.