Google Chrome perform HTML Import (Polymer) multiple times

I have an issue in Google Chrome. Included html imports are loaded twice.

Chrome makes 2 request to server, but the javascript in imported file is run once. As a result it breaks the CSRF protection, because token is generated twice for each request, and Chrome puts only first file content with outdated token.

This situation occurs only when DevTools are opened.

Checklist done:

1. Import is not duplicated
2. Firefox and IE make one request
3. JS console.log in imported file: logged once
4. Enabling and disabling cache makes no difference