Which ones? I thought being able to buy securities immediately after initiating a transfer before that transfer settles was industry standard? I know (at least) Fidelity and Vanguard let you do so with just a normal run-of-the-mill brokerage account.

My husband once accidentally messed up his transfer to Vanguard and it didn't go thru and he already purchased mutual funds with that money he meant to transfer. It told him he had a trading violation and the lady on the phone said having just a single trading violation didn't matter.