[teddyh]

If I throw some money in the air towards a group of people, who owns it before one of them catches it?

I would guess that I still own it. In the same way, you still own the bitcoin until someone else does.

[sneak]

When you throw money and it's floating in the air and not in your hand, you can't spend it.

When I leak a private key and the coins remain unspent, I can still spend them.

Tossing money into the air clearly ends my ownership of it. Pastebinning bitcoin keys does not (at least until someone sweeps the coins somewhere else using that published key).