After further evaluation I have found that the jump to scale as opposed to the smooth scaling happends when the new size is larger in both the x and y dimensions.

Meaning that if I scale a movie clip from 80,80 to 40,40 its smooth and if I scale a move cip from 40,90 to 80,80 its smooth as well. But if I scale a movieclip from 40,40 to 80,80 it instantly jumps to 80,80.

So to recap the scaling jumps instantly to the new size without smooth scaling if both the x and y sizes are larger on the finishing size.