When a checkbox is required on a form, "required" message isn't shown
This afternoon - while we were testing out several forms - my team came across this issue where a required checkbox didn't display the "required" message when the field was left blank:

Instead, a red box is shown around the field. I suspect this is a bug - that hopefully Marketo is aware of? Just now, I saw that @Sanford Whiteman posted a blog post that provides a temporary workaround: http://blog.teknkl.com/forms2-bug-checkbox-error-msg/