I reported that a few days ago in a ticket this was Adam's response
You're right this shouldn't be happening and a user shouldn't have to clear their browser cache.
We're trying to track down the cause - it seems to happen for a very small subset of customers but those for whom it does happen have the problem consistently. The issue is that the old session cookie isn't being replaced by the new one when the sign-on URL is hit.
We think opening in a new tab might resolve the issue. This is coming in one of the next updates