Ameritrade email answer:
Thank you for taking the time to send your comments to TD Ameritrade. I do appreciate the feedback regarding this restriction.
CXAC is restricted because they currently only trade in physical certificate form. TD AMERITRADE does not accept opening orders for securities whose ownership is recognized by physical certificates only. However, you may continue to place liquidating transactions for any such shares held in your account.
When companies convert to physical certificates only, it is difficult for brokerage firms to obtain physical shares for their clients. Converting to physical delivery also increases the costs associated with transferring ownership of common stock between buyers and sellers.
TD Ameritrade has made a business decision regarding restricting transactions in HESG. You cannot purchase this stock through us; however, you are welcome to sell any existing shares. Both you and TD AMERITRADE take on risk whenever a security is traded. While you may be willing to accept any risk associated with this security, there are certain business risks TD AMERITRADE chooses not to accept. I do apologize for any inconvenience.
I'm not a broker, paid promoter, or officer of any company. Nor am I responsible for you listening to my awesome opinions. :-p ASK and ye shall receive!