If you attempt to type your username & password while the page is loading, it'll keep trying to clear & refocus the username field. It forces you to wait for 5 to 10 seconds before you can use it. If you are typing without looking at the page, you will often end up entering a part of your password in clear in the username field. If you're impatient, you might even hit enter accidentally and send your password as your username to the server. Yahoo mail used to be like that, haven't used it in a long time.
If you attempt to type your username & password while the page is loading, it'll keep trying to clear & refocus the username field. It forces you to wait for 5 to 10 seconds before you can use it. If you are typing without looking at the page, you will often end up entering a part of your password in clear in the username field. If you're impatient, you might even hit enter accidentally and send your password as your username to the server. Yahoo mail used to be like that, haven't used it in a long time.