The explanation of this SPR is very clear "If any activity has resources assigned, then its 'status' will be rolled-up from resource assignments." This is exaclty how the feature is intended to work and should not be considered an SPR.
To change the value of the Plan Activity's status, you must change the status of one of the resource assignments. This can be done by the owner of the Resource Assignment or the Project Manager.
If there is a desire to set the status of the Plan Activity independently, then the resources assignments should be removed from it.
