While creating TCERs from a Test Plan, why are all Environments getting listed?

While creating Test Case Execution Records inside a test plan, when we get to Step 1 of the wizard, under Reuse Existing Test Environments the list initially shows just the environments associated with the plan but then it switches to showing all the environments setup in the Project Area. Which is the design intent? Show only the environments associated with the Test Plan at Step 1 or show all environments in the Project Area?