That is not an issue with the controller. The P3S has a "feature" that locks the stick in the full down position. You need to manually push it back up to release the lock. I don't know what the intent of this was other than perhaps to allow for a descent from high altitude without needing to keep pushing down. To me it seems more like a peril than anything else.
If you don't like the feature, you can open the controller and remove the clip that locks the stick in full down position. I think it is just two screws that holds it in.