Other mistake: When the invitation to the Hunt Ball is shown on the screen, it says that the ball is on Thursday, March 7, but on the night of the ball when Lena gets the telegram from Johnnie, the date of the telegram is March 8, 1938, which would have been the next day. And March 8, 1938, was actually a Tuesday and March 7, 1938 (the day of the Thursday Ball), was actually a Monday.
Continuity mistake: When Johnnie and Lina arrive back from their honeymoon, they decide to have tea and cake in their new home. Johnnie picks up the tea pot and starts to pour the tea, but then he picks up the tea pot for a second time and starts again to pour the tea.
Factual error: All the light switches are the wrong way round for UK, where up is off. Presumably because film sets were in USA.
Continuity mistake: When Lina goes to visit her writer friend, she opens the gate, then closes it behind her. But when she leaves, the gate is open.
Continuity mistake: Johnnie, Lina and Beaky are playing anagrams. Lina spells out the word MURDER with an M as the first letter. The shot cuts away and then back again, and now the first letter is an inverted W. (01:01:40)
Answer: It could have been body doubles, who are often used for filler scenes like this, but there's no way to know for sure.
raywest