Players have been intentionally abusing the bug that siege engines cannot be used at low HP, while aware that they also cannot be repaired. Trivializing keep raids by shooting all defensive siege engines down to 5%, at which point they can no longer be used but also not repaired, meaning the keep/tower is without its siege engine for defense.
I have screenshots of a recent keepraid in which this bug was exploited intentionally to prevent defenders from using the keep siege engines to destroy the ram and/or kill players standing under the oil at the CK.