The appellant shall not, except by leave of the Court, urge or be heard in support of any ground of objection not set forth in the memorandum of appeal; but the Appellate Court, in deciding the appeal, shall not be confined to the grounds of objections set forth in the memorandum of appeal or taken by leave of the Court under this rule:

Provided that the Court shall not rest its decision on any other ground unless the party who may be affected thereby has had a sufficient opportunity of contesting the case on that ground.