The glebe which shall be declared as aforesaid to be the glebe of the parish erected quoad sacra shall not be subject to the provisions of any trust constituted in terms of the recited Act, subject to this proviso, that if a manse and offices are erected on such glebe, either before or after decree of disjunction and erection or decree as aforesaid, the site of such manse and offices shall be subject to the provisions of any trusts constituted in terms of said recited Act.