HTML validation errors on page with list of user in usergroup

Steps to reproduce:

1. Login on forum as administrator.
2. Click on the menu "Administration" -> "User Groups".
3. Сlick on the name of group with 1 and more number of members.
4. Copy source code of the page, paste it on http://validator.w3.org and validate page.

Actual results: validation shows errors.
Expected results: validation shows no errors or warnings to show.

If if there are no users in group, validation shows no errors.