Maybe LC decided they don't need the potential bad press that could come from someone's tax cheating before their IPO?
That's a possibility. But how is that issue solved by very quietly prohibiting it and not enforcing anything? How would this newspaper headline look right before the IPO:
Lending Club makes possible biggest tax cheat in decades -- User agreement says not to do it That doesn't make them look any better, does it?
Regarding self-dealing in general... It's rather easy to do "accidentally", since LC doesn't show you seller names. It might be one of your other accounts. Maybe you didn't even post the listing (IR auto sell).
As far as I know, legally there's nothing wrong with self-dealing as long as the price is fair. And who is to decide what's a "fair" price? Not LC or the IRS. If it was easy to calculate then prices would be tighter. It's not all that easy. Maybe $1 seems like a fair price to me. Yeah that's the ticket. They'd have quite the battle on their hands trying to prove otherwise beyond a doubt. I have data showing that people have sold on-time notes for -99% before. You might call it seller mistake but prove it. Those past sales would boost my argument that it's not all that unusual. I wouldn't want to be sitting in the defendant's chair though.