Plane Sailing
Astral Admin - Mwahahaha!
It fundamentally doesn't make sense that you can make a saving throw, which essentially benefits you, to acquire a condition which you already have acquired. Logic, too, dictates that if you've fallen down, you can't re-fall-down without getting up.
I'm not sure that I follow your reasoning here.
It makes sense to me that someone who is prone can still 'grab onto something' to stop them being moved. The standard "saving throw to become prone and stop the movement" seems to me that it represents throwing yourself down and grabbing onto something. If you are already down when someone else tries to push you, you can still grab onto something.
This looks like a job for customer service, to me.
You're joking, right? Right?

I think I'm likely to house-rule that if something is attempting to force move you, you can make the save to stop the movement. If you have anything nearby you can realistically grab onto (railing, statue, table) and have a free hand, your save negates the movement and you are still standing. If you don't have a free hand or you've got nothing you can realistically grab onto while standing up, then you get to drop prone and stop the movement that way.
While I'm at it, I'll probably give the dwarvish 'stability' bonus to anything with 4 or more legs too, so they get moved one less square. Their extra legs *must* make them more stable than dwarfs, surely!

Cheers