During the rehearsal of the song "I Get A Kick Out Of You" at Cole Porter's mansion, a butler uncorks a bottle of champagne. The force of the uncorking knocks the towel off his arm. A second later in the next shot, the towel is back on his arm.
When Cole Porter talks to his mother at Christmas, he places his gifts on a table, and a long, thin box is leaning against other packages. When the scene cuts to show the packages again, they are neatly stacked.
It is implied that the U.S.S. Lusitania was sunk the same night as Cole Porter's Broadway play "See America First" debuted. In fact, the Lusitania was sunk over 10 months before (May 7, 1915) the play opened (March 28, 1916).
"You Do Something to Me" is depicted as being performed in "See America First" (1916) when it actually was used in "Fifty Million Frenchmen" (1929).
The poster showing one of Cole Porter's musicals reads The Gay Divorcee (1934). It should have read "The Gay Divorce". The movie was the former.
Throughout the film, Cole Porter is portrayed as a ladies' man, when, in reality, he was openly homosexual.
As in Kiss Me Kate (1953), Cole Porter is depicted as a healthy man who is capable of walking for most of the film. In fact, he was a cripple needing constant medical care for his shattered legs which were the result of a riding accident in 1937; any scene showing him walking after that date is in error.
At Christmas when Cole Porter goes home, his mother presents him with the sheet music to "An Old Fashioned Garden" that was published in 1919. Before this, a group of carolers sings "In the Still of the Night", which wasn't published until 1937.
In almost every crowd scene, no matter what era it is supposed to be taking place in, there are at least one or two extras wearing 1940s clothing.
When in England, there are street performers singing "Rosalie". The accordion player's hands never press the keys; in fact, his right hand is static throughout the whole scene.
When Cole Porter sings "In An Old-Fashioned Garden", the camera moves through the room towards the window. As it is approaching the window, a chair in the camera's way can be seen being pulled out by a crewman.
In England, after his show, Cole Porter buys some fries. He starts eating, and walks off without paying for them.
Although Porter was born in Indiana, Cary Grant makes no attempt to mask his inimitable British accent.