New Client Bug?

I was having a bit of a stress rush because every time I was trying to get into my account it would tell me "Username or Password does not match". I started thinking of all the passwords I know just in case it was just me being dumb but then I changed to the old client and it let me in first go. I then thought to myself "Oh hell yeah I remembered my password". But when I booted up the new client and tried the same password it tells me "Username or Password does not match".

I was logging in and off of the new client just fine but couldn't log in on the new client. " Cross Over "