Middle clicking results in navigation not new tab

[dgl]

On http://www.polymer-project.org/docs/start/getting-the-code.html if I middle click on e.g. "Using elements" on the left hand side (under Getting Started) it navigates the current page. I'd expect it to open it in a new tab (right click and open in new tab does work).

This is on Chrome 33 on Linux.

[ebidel]

Dupe of Polymer/old-docs-site#398