This is being abused constantly with new upkeep system. What happens is whether an attacker is succesful or not, as soon as the abttle is one they can be attacked by an army of 1/3rd its size. The trouble that makes it so glitch-prone is that all attackers images show attack only option on fiefs so they HAVE to refresh their page before entering a fief, whereas the 1/3rd size army can attack instantly and will always win the race. In this way clans are atatcking with naked armies to drain away enemy troops of gold and then troops through upkeep with no real loss. Even if auto-retreat is fixed to take away troops and equipment, this lame game glitch will be still overused by clans that rely on game glitching to win.
Solution: Random 5-10 minute cooldown after an attack allowing an attacker or fief to not be instantaneously attacked by another army.