The Button widget is removing the type
attribute from the Cancel button.
This makes that button behave like a submit button.
There are many possible paths to make this work. I'll start from simple to complex. The first is to avoid the issue entirely and not use JavaScript at all. Just use a link:
<form action="/Administration/Department/Create2" method="post">
<button class="yui3-button">Save</button>
<a class="yui3-button" href="/Administration/Department/List">Cancel</a>