Call it a 'change of design'.
It's a consistent and logical behavior since cmd/w closes that particular window which is in focus.
I like it that way
Thank you for your post.
This is a design change in FileMaker Pro 15, as Command-W will only close the Script Workspace if no scripts are active.
However, I do see that the menu does not change under Mac OS X when no scripts are open/active (the menu is updated under Windows). I have sent this information to our Development and Testing departments for review. When I receive any feedback, I will let you know.