Selected underbar does not appear when revealed from core-collapse

[rhashimoto]

If I put a paper-tabs element inside an initially closed core-collapse element, it does not indicate the initially selected tab (with a colored underbar) when revealed. The underbar is correctly shown when the selected tab is subsequently changed.

Here's a jsbin showing identical paper-tabs contents, one at top level and one inside core-collapse. When the button is clicked to open the core-collapse, the selected underbar is missing from the first tab on desktop Chrome 39:

http://jsbin.com/moqigi/1/edit

[rhashimoto]

This appears to be a duplicate of Polymer/paper-tabs#37 (Invisible selection bar).