If you attempt to log in with an incorrect password, and then log in again with your correct password, you do not get redirected to the admin page. You only see a screen message that says "You are now logged-in as admin." What's more, the login form does not disappear.
I've tested this in IE6 / Win, Firefox for Mac, Camino and Safari.
I suggest filing a bug about this issue at [url]http://open.silverstripe.com/[/url] (register, login, then click "New Ticket). That way the core developers won't accidentally miss it in these forums. ;)