By default, if we see a price get hit anywhere in the world, then we convert all your autotraders to a market order. This keeps everyone in sync. The downside of this is that during volatile periods, such as the exact market open, an order may be filled at your limit price, and then quickly move away.
If you find this happening often, based on the type of stocks you trade, you might want to consider changing the Fill Algorithm that C2 uses for your system. There is an optional setting that you can select, which tells C2 to NOT fill your limit orders UNLESS a real-life autotrader who is following your system gets the fill. There are tradeoffs for this - if you only have a few autotraders, for instance, and you tend to put in limit orders that are "just touched" (i.e. do not trade THROUGH the limit price), your system may not get a fill.
If you are interested in using this setting, go to Manage -> EDIT SYSTEM (from your main system page) and scroll down to "Fill Algorithm".