Yes, the Redirects tool in the control panel has the tendency to do this. You may want to use the Redirects tool in the client area instead, it’s more robust.
To clear out the current redirect, you can simply edit the .htaccess file of your site by hand. In the htdocs folder of the site you’re trying to set the redirect on, you can simply edit the file called .htaccess and remove the relevant line that starts with RedirectMatch. Those lines are created by the redirects tool.