I have been using a cash -- i.e., no margin -- Ameritrade account for most of my trades for the last year.  Not a big deal, but something happened last week that I don't recall happening before. 

I had a small amount of funds in a money market sweep account.  I put in an order to sell one security and then immediately used most, but not all, of the proceeds to buy a different security.  Toward the end of the day, I attempted to electronically transfer part of the funds in the money market account to my checking account.  I have made such transfers numerous times without incident.

However, this time, I was advised that I did not have funds available for the transfer.  It seems Ameritrade used my "settled" funds -- the funds in the money market account -- to pay a portion of the cost of the new security I bought and the remaining funds in my account would not be "settled" and available for withdrawal until the settlement date for the sale I made.

I have a general understanding of Reg T settlement issues.  I did not understand that Ameritrade was obligated -- as they have now claimed -- to first apply my settled funds to the purchase transaction.  Does anyone know if this is true?  Thusfar, I haven't found a reg -- or even a disclosure on the Ameritrade website -- that says this is required.

The lunacy of this policy is that if I had transfered the funds at the beginning of the day and made the sale and purchase afterwards, all would have been fine and I would have had my funds three business days ago.   As it is, I have had to wait three days to access my funds.

As I said, not a big deal, but frustrating.