Some may believe that the mouthpiece ligature on the tenor saxophone that Eddie Cook (Sidney Poitier) plays is upside down. However, in the first scene when the band is playing, it can be seen that the thumbscrew that adjusts the ligature is on the bottom, where it normally would be. It is, therefore, not upside down.
Even though Sidney Poitier was coached by the great Paul Gonsalves and with so many real saxophonists appearing in the film, the saxophone mouthpiece on Eddie Cook's (Poitier) saxophone is a very popular brand from the era (an Otto Link), the mouthpiece has a custom-made ligature formed to the mouthpiece, and it is upside down.
As the river boat scene ends, Ram looks over the bow of the boat, but the very next cut is to a trailing wake, which is at the stern.
When Louis Armstrong and his band come into the club, the patrons are clapping to the wrong beat. The clapping on the pre-recorded soundtrack is on the second and fourth beats, while the patrons are seen clapping on the first and third beats.