- Block an account (settings on the block don't matter)
- Checkuser the account's IP address with "IP to users"
- Check the box next to the account's name
- Enter a block reason into the "block selected users" form at the bottom of the page
- Click "Block selected users"
The form will replace the content of the account's user and user talk pages as requested and expected, but the original block will not be replaced with the ACB-Autoblock-indefinite block that is expected from the form.