Account activation link doesn't work if username contains spaces

Account activation link doesn't work if username contains space, or contains more than one word

to reproduce:
1. click on "Sign up" link
2. fill username field with two words
3. fill other fields and click "Sign up"
4. Get link from email you recieved after new account registration and paste it in address bar of your browser, and press "Enter"
Expected result:
you should be redirected on main page, and be able to login with registred username
Current result:
you are on 404 page