Bug description

Browser "back" does not work after following a link with unpoly that contains an anchor starting with a number

Reproduction project

https://zesty-bubbly-samba.glitch.me

Steps to reproduce the behavior:

1. Go to reproduction project linked above
2. Click on 'Link to other page'
3. Try to return to previous page by clicking on the browser's back button
4. See Error: you are still on the same page but the navigation bar has been updated to the previous page

Expected behavior

Clicking on the browser's back button brings me back to the previous page.

Additional context

I did some research and found out, that in HTML 4 ids must start with a letter. See this stackoverflow answer and therefore querySelectorAll throws an exception if it comes across an Id that doesn't.