I had some Problems with a required Checkboxfield ("yes i've read the terms of use") in a form that wouldn't validate.
The Checkboxfield was listet in the RequiredFields array but the Form was sent with unchecked Checkboxfield.
There are 2 patches that solved my issue:
(Silverstripe 2.4.7)
Ticket #6231: check_box_php.patch
http://open.silverstripe.org/attachment/ticket/6231/check_box_php.patch
Ticket #6230: check_box_js.patch
http://open.silverstripe.org/attachment/ticket/6230/check_box_js.patch
...maybe it helps anyone, it wasn't easy for me to find them...