As far as I can tell, this is down to browser bugs to do with the fieldset
element.
It's a known issue with fieldset
elements in Chrome. Firefox has a similar (very old) issue in that legend
and fieldset
are replaced elements.
I guess it's safer to use a <div role="group">
instead of a real fieldset for now. In your CSS you could use div[role='group']
as your selector. See http://www.deque.com/aria-group-viable-alternative-fieldset-legend for more information.