I noticed this too, and finally figured out the inconsistent behaviour.
If the car is locked (padlock icon is closed) then switching into "park" extends the handles.
If the car is unlocked (padlock is open) then switching into "park" does not extend the handles. You need to press the park button again to extend the handles.
If you have drive-away locking enabled then if you only drive a short distance the handles won't auto present (because the car hasn't locked itself yet) and if you drive a longer distance they will.
If you don't have drive-away locking enabled then the handles won't auto present - giving more consistent behaviour but does mean that anyone can open the car from outside if they know they need to push in the handle first.