At night at the kennel club, the lights over the bleachers go dark before the dog race starts, yet the shots of Tony and Jerry talking are still brightly lit.
When Ally is shown running back along the street calling for his father at the end, in the distance the taxi is seen making a U-turn while a large crowd of onlookers stand on the streets behind it, obviously watching the scene being filmed.
Although Manetta is an Italian name, Sinatra and Robinson both speak with a New York Yiddish cadence and phrasing (e.g., "I should drop dead on this spot!"), though of course only Robinson was Jewish in real life.
The final scene includes several shots looking out across the beach towards the ocean and there are some hills evident along the distant coastline which does not match the topography near Miami Beach, Florida. This was shot at Hollywood Beach, Oxnard, California.
When Shirl goes surfing at night, there is a tall island on the horizon. There is no such island offshore from Miami Beach, Florida. It is the Channel Islands, west of the actual filming location, Hollywood Beach, Oxnard, California.
Only in a Frank Capra movie could a swinging bachelor share a bedroom with his 11-year-old son.