It shall be the duty of the appeals board to determine in the case of members of the California Highway Patrol, upon request of the Department of the California Highway Patrol or Department of Justice, and, in the case of the harbor policemen, upon the request of the San Francisco Port Commission, whether or not the disability referred to in Section 4800 arose out of and in the course of duty. The appeals board shall, also, in any disputed case, determine when such disability ceases.