That doesn't seem normal/by design and I wouldn't consider it expected. I have a similar configuration and I've never had to login or reconnect after the initial configuration. If you weren't using the same SSO domain at both sites you might have to login like you do in your 5.1 environment, but with the same domain you definitely shouldn't have to.
That said, I don't know what would cause this. I would suggest opening an SR and looking through your logs.