I've never had a broker call and ask me to "bust" a trade, I've always had to call them. But IB used a live person to call me and ask if I wanted to bust a trade at Island for 200 shares! I shorted 600 shares and was filled on 2 exchanges at 16.50 and on Island at 16.00. Is this normal for IB with their bare bones system to care about my fills? I decided not to pursue busting the trade, but was impressed at the customer service.
If could have been that the other side wanted to bust the trade and IB called to ask for your permission. this has happened to me several times.
That's possible, but it was in the other sides favor $100, and he didn't mention that the other side wanted to bust it.