@simtrader I appreciate the lengthy explanation. Essentially, yes with CQG Bracket Orders do not reside on CQG until the limit order is filled. So far our experience has been (with CQG) that when one order is filled, the other is canceled. Although your explanation is using Sierra, we assume the same is true for CQG with Multicharts where the OCO will kick in only when the limit is filled. The OP is a Multicharts user.
Having said that, there are those who insist on Bracket Server Side OCOs when the entire bracket sits on the server and not on a personal computer. There could be an instance of a drop on the internet, and then you have no protection if the bracket did not go in. Clearly, for those who are afraid of this one-off event, it is a source of comfort. Having said that, you raised a good point. Bracket Server Side OCOs are tricky and need to be implemented right, and clearly, this is not always the case. Further, the server the OCO resides on could fail. Then what? Having a trade-desk number is always a great source.
The only true thing you can rely on is native exchange orders.
As an FYI, some of our users who use the RIthmic feed, use R Trader for the server bracket OCOs while using the Rithmic feed to also fuel the charts of their application. We need to check whether the R API+ by Rithmic does provide bracket server side OCOs on Multicharts because on Sierra it does not.