Polymer: scrollbar underneath scroll core bar?

As of 2014-10-22, the title bar of scroll-bar widget is drawn above the top of the browser scroll bar. This is deeply suboptimal as it can make the thumb completely inaccessible until you scroll down. (And first you should notice a scrollbar there.)

The standard Polymer widget demo demonstrates this:

https://www.polymer-project.org/components/core-scroll-header-panel/demo.html

This happens in both Chrome and Firefox.

Does anyone know of a workaround?