Dr. Huntington Bailey rings a doorbell at street level, but when he steps through the door into his friend's apartment, they are on an upper floor.
In the long shot when the principals go in to dinner, the butler closes the door. The next shot, a medium, shows the butler closing the door again.
Towards the end, when Dr. Bailey attacks Nick and the two briefly fight, it's obvious that the people fighting are stunt doubles. Nick's stunt double has a different hair color.