Zecco used to throw up 'DTC chills' all the time.  They 'merged' with TradeKing.  The issue with Zecco was Penson.  Penson had some serious financial problems -- eventually leading them into BK.  It always seemed suspect which stocks they decided to chill and which they did not.  To me.  Then again, I'm a suspicious person!  It's just that all the chills started coming to pass PRIOR to the 'news' of their financial issues.

Anyway, Zecco always blamed Penson, their clearing firm.  Zecco lost a lot of customers from it -- probably why the merger w/ TradeKing.

I believe TD clears for itself -- possibly why we are only seeing the chill issue with TD.  Chills are related to clearing concerns.  Correct me if I'm wrong about this.  I don't use TD.