Well it might not be as much as a bug as just a matter of system priority.
I gather you are using Mac OS X, but for just about any operating system the same principle applies. Different applications can typically be given higher priority than others in the 'Z-order', this means that if a low priority application tells the OS to bring it to the front, the OS may decide that it should still appear behind another application that has a higher Z-order priority.
All this means is Express Talk probably has a low (default) priority and that for whatever reason iTerm considers itself to be higher in the food-chain. NCH could probably bump up the priority a bit considering a phone call is pretty important, but I wouldn't really call this a 'bug'.