I had that problem a while ago, If I remember correctly, Android was sending "cookies:" and not "Cookies:" in the header.... so setting cookies via arc or js was great, reading them with js was also fine, but arc couldn't parse them from the header.
Nevermind. Looks like its a known issue. it appears logins don't work from web interface, rather one has to create an andriod app to handle the authentication to the page.
curious - does the browser not handle cookies, or do you know why this is an issue? Do you mean every web app that requires a login needs a custom app in order to be usable on an android? (I know nothing about android, count me a total noob)