Oh, please. I am sure that ALW has stolen MANY melodies from Puccini's Madama Butterfly for his own musicals!
Well, if you listen to any of the Meyerbeer operas, you'll hear lots of familiar melodies.

-And since Meyerbeer operas are rarely performend, well... Maybe that's "why", if you get my drift.
However, the "Humming Chorus" in
Madama Butterfly has always reminded me of "Bring Him Home" from
Les Miserables and vice versa - especially when the barricades are spinning (in
Les Miserables, that is) showing all the dead bodies, with the oboe playing the melody and the strings/keyboard sparsely accompanying.