about 5 years ago - I had the same problem with IB -
Quote from Toonces:
Is there any way to prove that you didn't place an order through IB? For example, let's say you place a limit order to buy at 10.00, and you get filled at 10.20. You call IB, and they tell you that you placed the order to buy at 10.20. Aside from recording your screen during trading, it seems like you have to take their word for it. (An audit trail really wouldn't help.)

Quote from GTC:
alanm, I am not even talking about changing an order after a partial fill. Those two simple examples are very clear cut. IB transmits those order without difficulties. You will find out those discrepancies in Trade Summary. It were not even the cases in which TWS thought an order was just partially filled. The point is IB's order accepting system does have annoying bugs that can change the user defined inputs without valid reasons even long after accepting and transmitting the orders.
Quote from GTC:
consider the following 2 orders
Order1:
---------
(original order) ABC stock 300share BUY LMT 28.0
(attached order) ABC stock 200share BUY LMT 27.0
Order2:
---------
(original order) PQR stock 400share BUY LMT 26.0
(attached order) PQR stock 500share BUY LMT 25.0
You should be able to attach an order as in my examples.