I was trying to use a simple checkbox on a form, so I just copied the sample from bootstrap. But I forgot that I was using FuelUX on that form, so it never showed the checkbox. Apparently, there's a problem mixing checkbox controls -at least in this case-.
So, my form was like this
<form name="editForm" role="form" novalidate>
<div class="fuelux">
...
<div class="modal-body">
<div class="wizard" data-initialize="wizard" id="myWizard">