Standard button element not clickable in paper-header

[torsjonas]

A button element is not clickable when placed directly inside an element having the paper-header class. However, wrapping the button in paper-material makes it clickable. Don't know if this behavior is a bug or a feature, but it was not what I was expecting.

Some partial code to clarify what I mean:

With the following html the button is not clickable:

 <paper-scroll-header-panel class="fit">
   <div class="paper-header">
     <button onclick="foo()">Foo</button>

With the following html the button is clickable:

 <paper-scroll-header-panel class="fit">
   <div class="paper-header">
     <paper-material>
       <button onclick="bar()">Bar</button>
     </paper-material>

[blasten]

The docs is missing that the class should have position: relative | absolute http://jsbin.com/sijedo/edit?html,output