A closer look at Ameritrades policies regarding settlement restrictions shows this:
"The following example illustrates activity that will result in an account being restricted:
A client is holding $10,000 cash in a cash account. The client then makes the following transactions:
The client buys a position in Company A for $10,000, applying the $10,000 in cash to pay for the purchase.
The client then sells that position in Company A and nets at least $10,000 in sale proceeds.
Next, the client buys a position in Company B for $10,000, relying on the proceeds of the sale of Company A shares that have not settled to pay for the purchase.
Before the sale of Company A has settled, the client sells the position in Company B and nets $10,000.
In the above example, the client sold Company B shares before paying for them. Trading in this manner in a cash account may result in a 90-day restriction, limiting purchases to the settled cash in the account on trade date.
These restrictions may be avoided by
Adding funds to your account;
Combining accounts; or
Converting to a margin account*.
So that definitely answers my question.
greed_kills, looks like I should have just gone ahead and sold that tanking issue. I hadn't read it accurately the first time as it says it may result in a restriction to cash but wouldn't freeze the account.