In the case where a client is given the okay to sell prior to the brokerage receiving "clean certs," it appears (depending on the brokerage) that the client may be forced to buy back shares if the stock is later determined to be non-transferable.
I assume this could be "invoked" at such times as this where the stock shows up on Reg SHO for successive/excessive FTDs.
I further assume-- if invoked -- this phenomena would present similar trading characteristics as a short squeeze (if the amount of shares were large enough to create a demand pressure).