Yes, it's a 'gaffe' obviously due to numerous takes of the same scene. I noticed long ago how Kay's cig changes lengths throughout and sometimes is not in her hand at all.

I've learned to ignore it...what bothers me much more is how anyone can eat lasagne and be smoking a cigarette at the same time. Absoltuely gross.

Another similar one though not quite as blatant is when the baker is seeing Don Corleone to ask for Enzo's citizenship. At alternate moments he's holding a demitasse glass and then he's not.

Apple