trouble focusing with GH2 and 100-300

I believe I found the problem. Pre AF or Pre Auto Focus

If I turn it off, use neither Q-AF nor C-AF, I no longer have the issue. It seems the pre-af can't really tell what I am attempting to target with the smallest focus point. Since its prediction is off, it is fighting me and even refusing to change its predicted target if the predicted target is still obtainable within the small focus square.

I can successfully use AFC or AFS when targeting even blades of grass or skinny twigs that only go across the focus box.

Like at the edge of a pond, Pre-AF will focus on the background lilly pads and water 30 feet or more away and refuse to adjust to the slender fussy (out of focus) twig in the focus box no matter how many times I half press the shutter. Set Pre-AF to NO and it readily focuses on such items when you half press the shutter.

I can't believe how many shots I have missed, the true subject only partially in focus due to this.

Edited to add...

I remember a thread regarding the claim of a back focus issue. In a way that is what this was. I wonder if that persons backfocus issue was simply PRE AF predicting the wrong target and just not adjusting.