Two GIs are in the basement of a European house with a butler. They finally decide to escape. They escape to a movie set of WWII and find out that the war is over. They go to LA and write a book and the butler follows them to LA.
I believe you are describing the 1965 movie "Situation Hopeless...But Not Serious", with Alec Guinness and Robert Redford.
In it, two aviators are forced to bail out over Germany. They are hidden in a cellar by a friendly German who enjoys their company so much that he lies to them letting them think the war is not over after it ends.