Thanks for contacting World Warfare Support.
We have been made aware of an issue with an exploit where you can activate a shield on your city for protection, while being under attack. (Note that it is intended by design that the protection shield can be activated once and lasts for 8 hours and as long as you do not attack an enemy your city remains shielded.)
Also note that being able to activate a shield during battle, even after changing the way the game system identifies and handles this feature after the latest update is what we have been having our team investigate and our QA guys trying to reproduce this bug. Our developers and engineers have worked on many variations of fixes for this by changing the rules and some tweaks to the calculation timer that determine when and how the protection shield is activated, and this should be fixed in this week's update.
We appreciate your patience and again, apologize for the inconvenience.