Jimmy wasn't dubbed, but he was censored! Here he is, singing the uncensored lyric of "Easy To Love" in "Born To Dance" with Eleanor Powell.

Proof positive that the Hays Code went too far. How could anyone find this offensive:

"So sweet to waken with, so nice to sit down to eggs and bacon with..."

Pretty shocking, huh?

From Mark Steyn:

Porter suggested a lanky boyish actor on his way up: Jimmy Stewart. Jack Cummings liked Stewart but didn't think he could sing. So the next day Stewart came round to give his pipes a work out for Porter. "He sings far from well, although he has nice notes in his voice," wrote Cole in his diary, "but he could play the part perfectly." A stage-and-screen composer makes such compromises all the time. The advantage Stewart had over William Gaxton was that he didn't know enough to know the song had too wide a range for him. Unaware that he couldn't do it, he just got on and did it.

The trick is the verse. The chorus has an easy confidence and, while that's fine if you're Sinatra launching into a ring-a-ding-ding arrangement with Johnny Mandel, it might not be entirely convincing for an actor who became the master of small-town semi-stammered diffidence. But Porter's verse sets up the situation perfectly. Stewart and the unlikely object of his affection are strolling through Central Park, and suddenly there he is - Jimmy Stewart's singing, and the high voice on the Cs and Ds of "care for me" are utterly charming.

This being Hollywood not Broadway, Porter's couplet about being "so sweet to waken with/so nice to sit down to eggs and bacon with" was taken by the producers not as an affectionate paean to domestic routine but as the aftermath of an incendiary night at a hot-sheet motel. So he was prevailed upon to make a substitution:

So worth the yearning for
So swell to keep ev'ry homefire burning for...