I think this could be an air bubble under the scleral.
When the cornea is exposed to air, it gets its oxygen from that, and a little bubble's oxygen will soon be used up.
The cornea will then start taking on water for oxygen, and that causes odema (swelling) and cloudyness. I'm not really sure why this doesn't happen anywhere near as fast if the bubble is completely absent, but you must try to be completely bubble free.
Make sure that your head is pointing down so that your face is horizontal... then look down some more so it feels as though you're upside down (you're probably not

If you do keep on getting bubbles, it's worth trying a lens with a vial of Celluvisc instead of saline. It's so viscous that bubbles don't form so easily, and it doesn't spill so fast either. Ken at Moorfields suggested that to me, so I'm sure it's safe.