From the 1.07 Readme:
5- If you fight in a region where you have a structure, you will now retreat inside.
Seems to me that this is not wise. The last place you would want to retreat to is a structure in the area where you just lost a battle. You are immediately besieged and as good as dead. Game over for Washington and the Colonial army. If there is a friendly controlled area adjacent, you should retreat there. This is a game breaker which dooms whole armies to annihilation.