With Windchill 10.2, a Product or Library has a Tasks page you can reach through the Navigator Panel. In reality there are 2 Tasks pages and only one of them is shown based on an OOTB validator. The validator decides which one to show based on if there is a Plan created on the Product/Library or not.
The difference in behaviour between the 2 Tasks pages seems to be about showing the Plan Activities in the Task list along with workflow tasks or not.
There are use cases where business users strongly request for the original Tasks page to be maintained even if a Plan is created on the Container. Today in Windchill 10.2 the only way to do this is to customize the OOTB validator. It would be better if PTC provided a preference that could control which Tasks page is shown. Preference could be :