Keeps and towers can be kept in the "Under Siege" status indefinitely by enemy players if they want to. Just shooting a guard once and running away to stealth and doing it every 5 minutes is enough to prevent the keep leaving the "Under Siege" status, even if no players are actively trying to siege it anymore.
It prevents repairs and keeps the keep vulnerable to a new attack, while defenders have zero chance to prevent it. A single player with longshot is long gone before anyone can figure out where they are at.
It breaks the game and prevents repairing keeps after a successful defense.
Suggestion: Remove that attacking normal guards triggers the "Under Siege" status and make only gate damage count, thereby making it easier for players to prevent setting the siege status by observing and defending the gate.
Suggestion 2: Reduce the timer it takes to leave "Under Siege" status so repairs are possible more quickly.