Ya'know, I recently loaned some money to a friend's business. Called up a lawyer and had him write up some paperwork for this. His very first draft included a right of offset. That was easy. The prosper agreements still don't have the one sentence that would be required to make their right to withhold payments to late blenders clear.
Even without that sentence, prosper could have, with a small change to their web software, asked lenders who borrow to make their prosper account an authorized account for withdrawl (by prosper) of payments. After all, they already are set up to let members specify several accounts. The blender's prosper account is just another account. This would require no change to any legal paperwork at all.
Given that it is so easy to do the right thing, it is amazing that Prosper management chose to poke their fingers in the nose of lenders on this issue. They have no sense of what is right.