The biggest issue for BIF is shooting birds against foliage. Up to now it just does not work - although comparing notes in a hide earlier this year with Canon and Nikon users they complained of exactly the same problem. As the bird goes in front of trees, the AF just gives up and focuses on the trees. Oddly enough, it does not happen against lighter coloured foliage, like grains and reeds.
Hence the description of the change in AF being "There were cases where focus point was shifted to the background while tracking the subject in AFC mode. The new firmware minimizes this problem."
I'll be testing this at some point having downloaded the new firmware. To date, I am less than impressed with BIF photography with the G9+200/2.8. However, I have no frame of reference and I don't know what a good keeper rate is. My keeper rate is between 5-10% of BIF photographs.
I'm the first to admit that it could be operator error but after a while having beaten yourself up again and again, you begin to allow for a scintilla of doubt that it may actually be the camera.
I did discuss this with a Lumix luminary who does a lot of wildlife photography and he agreed that all cameras do have problems with BIF against foliage and told me that Panasonic are aware of the problem and hope to address it.
However, I just don't accept that this needs to be a problem in this day and age when computation and AI have reached such an evolved level. I think the problem is that camera manufacturers are not getting enough input from wildlife, especially bird, photographers explaining what the problem is. After all, once you are tracking an object, e.g. a BIF and the camera has locked AF, how difficult would it be to build in computation which says maintain this object as the key subject in the frame until the shutter button is no longer depressed?
I was going to go out to Buckinghamshire today and photograph Kites in flight but the weather is not good enough. As soon as it is I'll go back and see if there are any improvements with the new firmware. I hope there is because as things stand the new XT3 and 100-400 are looking very attractive to me at present instead of my G9+200/2.8.
Just my two cents
Louis