lets you to execute a command as another user (sudo)
Basically, you are still logged in with your regular user but that one single command after -s is executed by another user (root in your case).
$sudo -s ls -l // you are root on this line
$cd ~ // you are regular user on this line
This is the reason why you are getting redirected into the home of your regular user.
Doing such things in general is a bad idea, this is why Ubuntu disabled such forms of root login.
If you could give us a hint what do you want to achieve, somebody may figure out how to solve that without substituting your regular user shell with a root shell.