When you add a a new WAS profile instance in a workspace, what you are really doing is to create an "instance" of that particular profile in your workspace.
Now if you create a new workspace and add an instance of the same profile, since it is the same profile, the data sources are going to be there as it is still the same WAS Profile.
If you want to have the two workspaces to be completely separate from one another, you need to create anew WAS Profile (with a different port).