I think andrea is right and an overlap factor of 1 equals no overlap, how else could you have a hopsize the size of the frame size (try to picture it),

if you have an overlap of 2 then 50% of the samples are re-analysed next time (and calcluation happens every fftsize/2)

if you have an overlap of 4 then 75% of the samples are re-analysed next time (and calcluation happens every fftsize/4)

if you have an overlap of 8 then 87.5% of the samples are re-analysed next time (and calcluation happens every fftsize/8)

so

if you have an overlap of 1 then 0% of the samples are re-analysed next time (and calcluation happens every fftsize)