I asked TDA why and this is what they replied:
Some of the reasons a stock may be restricted to Closing Transactions Only
include:
Corporate Actions in which a lack of information, confusing terms, or unclear
objectives may be involved. All corporate actions should be transparent as to
objectives.
Apparent or possible fraudulent activity by a company or it's officers, with
potentially manipulative actions to affect a stock price.
Frequent unsubstantiated press releases in an attempt to affect the stock's
price.
Deceptive or contradictory statements regarding past or projected performance.
Corporate Identity Theft
Valid companies associated with 3rd parties (i.e. transfer agents, consultants,
etc) that have shown a predisposition to any of the above activities.
Companies known or suspected to be involved in Money Laundering activity
Some of the criteria NOT used to make this decision include:
Stock price of this security
Positions of our clients and the firm
TD AMERITRADE does not participate in the trading of non-listed securities in
it's own account for the purpose of making a profit.
Thank you,
Shawn D.
Client Services, TD AMERITRADE
Division of TD AMERITRADE, Inc