Never knew this until 30 years after I saw this movie...

In TOS, during the party scene at the Hilliards' home, June Allyson reminisces about when she started her singing career during WWII and how she met her husband (played by Leslie Nielsen). During this flashback, she sings "Young Man with a Horn" as part of a show for servicemen.

WELL - it turns out that Junie sang that exact song in her first real starring role in "Two Girls and a Sailor" (1944), accompanied by none other than Harry James!

So the flashback scene in TOS actually reflects real history!

"Don't call me 'honey', mac."
"Don't call me 'mac'... HONEY!"