HI JWW, Sorry I was not clear. This was paper and not the API. I just assumed the behavior might help you debug the system. Also I would not look for compensation from IB because there are so many disclaimers, it would be an uphill battle. Instead, I would debug, test in paper and make the money back in Live. If you are using the API, I assume you have a good system and confident it works under a lot of conditions, but then again, I don't know what the system does etc.
I do know some orders are held at the exchange, and some at the IB server. You can see the list at IB for each order type. I played around with different types of orders trying to get them to all be native on the exchange (i.e. no simulated), but came up inconclusive and moved on to more important issue. I will probably revisit sometime when it becomes important. Best of luck