Back button navigation somtimes broken on polymer-project website

[steren]

How to reproduce:

• go to https://www.polymer-project.org/
• click "Get Polymer" (it goes to https://www.polymer-project.org/docs/start/getting-the-code.html)
• hit the back button

What is expected:

• browser goes back to main page (the previous page)
  What happens:
• stays on the same page, I have to click twice to go to main page

Another occurrence of serious back button breakage:

• go to https://www.polymer-project.org/
• click Topeka
• hit back button

What happens:

• stays on the same page, impossible to go back to previous page, back button is stuck

[ebidel]

This issue was moved to Polymer/old-docs-site#741