You need to specify the talents that you want to use for optimizing now – otherwise allowing multiple setups per spec doesn’t work very well and gets cumbersome to use. We also found that a lot of people were importing from the addon with e.g. not their normal talent setup because they were questing or something, and then the optimization would change and they didn’t really know why.
The first time that you create a setup for a spec (which we do automatically whenever you activate that spec on the website and have no setup for it yet), it uses whatever talents you currently have in-game. From that point onward, you should explicitly set the talents you want to use for optimizing.