Chromium/Linux here, I can replicate it on the specimen page.

https://fonts.google.com/specimen/Noto+Sans

Under the 'Styles' section, type:

    `foo`

You'll see the first ` overlap the f.

Now erase it all and type:

    ````

They all overlap each other and show up as just one `.

Edit: from what it looks like, the problem is specific to the sans. I can't replicate it with the serif (https://fonts.google.com/specimen/Noto+Serif if anyone wants to try).

For me at least (Chrome), it seems like it isn't applying any surrounding spacing for the backtick. If you hit ` a few times and then hit some other character, they seem to occupy the same space in the text box.

I experience same problem with Firefox 47.0 on Ubuntu 15.10.