When Paul goes to put the candy wedding band on Victoria's hand, he has a wedding ring on. Then he reaches back into the candy box for another band and puts it on and his original wedding ring is missing from his hand.
After the serenade Paul walks through the vineyard and away from the house. The moon is behind him and casts his shadow before him. He turns to look at the house and faces the moon. Now here is a bright light on his back (from the direction he was walking towards).
When Paul and Victoria are looking at the view of Las Nubes, the sun is over the house (and therefore in front of them) in the shots of the house, but in the shots of them standing together, the light and shadows show that the sun is behind them.
While talking to his father in law on the balcony, Paul's hair changes repeatedly between shots.
When presenting her with wedding ring from the candy box, three candies had "wedding bands" on them. After he removes one for her and one for himself, the remaining "wedding band" changes places in the box.
There are no cable car tracks visible in the street scene. Cable cars run on tracks pulled by an underground cable.
At the beginning of the movie, when Paul is walking home, a woman wearing a blue Air Force uniform enters a building. The Air Force wasn't a separate branch of service until 1947.
The train locomotive is a General Motors EMD F7 first made in February 1949.
Although a version of the music that the German/Austrian band plays at the wine festival existed in the 1940s, the version played did not exist until 1975.
There is a scene of a country road with solid white lines painted along the edge. In the 1940's roads were not painted this way.
On first arriving at the vineyard, a Ferguson Tractor is shown sitting in a shed. Harry Ferguson did not begin producing that line of tractor until 1948.
As Paul is hitchhiking home south to San Francisco, a driver said he can take him as far as San Rafael. San Rafael is north of San Francisco. The car is also driving south (ocean to its right), which is correct. However, the coast is at least an hour out of his way to the west of Napa, and he would not have gone that way.