Ive noticed Ameritrade will not allow buying certain pinks/otc's more and more frequently and not always because of a "Chill". Ive asked them on a few, with rather vague answers like "it depends on this and that, best way to tell is try to put in an order".
Not that MDCE does not have a Chill, just be aware Ameritrade does not need a "chill" to limit buying certain ones IMO.