It's not obvious what the problem is, but at the start of the second song by Jehosophat and Jones, Ronnie Barker is clearly having problems with his comedy character spectacles, and misses the beginning of the song as he removes them and replaces them with his ordinary glasses. He then completes the section wearing his very normal looking glasses.
In the Phantom Raspberry Blower section, the Prime Minister, in 1899, welcomes representatives of the Commonwealth, which did not come into being until 1926.