I am experiencing an initial pop when trying to animate focal distance in the Sequencer.
The screen caps are the first three frames.
First frame normal, second frame kind of pops, third frame normal.
It does this regardless of the curve settings.
When played back it makes a flash when the initial focus pull starts.
Problem identified:
I was using extreme settings. Using a focal distance of 0. Seems to work OK with distances of say 3-4.
So it seems to be acceptable in this range. Probably a bug but I think this is an acceptable workaround.