Why was it not approved? Perhaps because of some notable resemblances to an earlier Impromptu (Op 89) by Ignaz Moscheles. Though the central melody is far more memorable than his predecessor’s effort, as the songwriters of I’m Always Chasing Rainbows recognised when they stole it.

Resources 

Watch pianist Chenyin Li perform the piece below for some inspiration!

Pianist Lucy Parham gives an in-depth lesson on the piece here.