No you’re right, if you have an edition without works the button is green and it works properly.
If there are already some existing works it looks like your pic and this definitely doesn’t work correctly.
Another issue that went past us !
Thanks again for reporting, and sorry we missed so many in the last update!
We’re working today on patching the bugs you’ve both reported in the past few days: ISBN issues, slow page when editing/creating an Edition, and this new one with the “add work” button.