After having reauthenticated for accessing the ACP the following message tells you that the reauthentication was successful:

You have successfully authenticated and will now be redirected to the Administration Control Panel

Click [u]Here[u] to return to the previous page

Clicking "Here" redirects me to adm/index.php which is not the previous page I have been visiting (it was /index.php). I think the text should be changed by replacing "previous page" with something like "Click Here to procced to the ACP" as this is what the link is actually doing.