I don't think there's a bug here, as fktifzobr@mail.ru believes. In fact, the opposite happens: the individual camera is disabled by the General camera when viewing the castle garrison.
The suggested solution of creating a copy of the General camera for everyone and placing the hero in the original camera would result in everyone except the hero becoming tiny in the garrison. Adjusting everyone to fit one giant is not the right approach, and it's also a scripting issue.
There probably is a file that specifies the camera for castle garrisons. If it's race-specific, there's nothing to be done, but if it specifies a General camera, it might be possible to add an individual camera or remove the General camera.
Where is the individual camera defined? - In the hero file for the map.
What happens when the hero hides in the castle? - His model disappears from the map.
I think the hero is removed from the map, but his model and stats are saved in the map's cache, but the path to the individual camera file is not saved