I spent a chunk of my IB Avios, then spent another chunk but cancelled the Avios booking. I transferred the balance in a couple of transactions, first direct to BA and then to BA via Avios.
Since the transfer I reckon that I have probably (although I am no longer sure) spent as many Avios on my BA account as were transferred, although as I had a very large pre-existing balance who is to say which were spent (first in first out, last in first out ??).
In any event, I have not received the warning e-mail. I am not sure what any of that means ......