At the moment the form HTML the buttons in WeBuilder output is often invalid. Some efforts need to be made to make these (and any other things that aren't validate) adhere to the doctype or global WeBuilder setting for XHTML 1.1.
For example, if you create a <form> element it puts method="POST". This is not XHTML 1.1 valid because it must be lower case, thus reading as method="post".
I'd consider this a borderline bug.