H1 focus question for large zoom

[ghostwheel]

I just got my H1 yesterday night! Just trying it out. I have a question:
It seems the camera behaves slightly differently when zoom is below 7x vs. when it is above 7x.
At large zoom, when I am focused on a subject (say because I just short a picture of the same subject), and press the shutter-release half way, the camera will do a short unfocus-focus. This happens even if the subject has high contrast. This unfocus-focus is quite noticable, and one can hear the motor move the lense.
Below 7x something else happens: there still is a short unfocus-focus, but it is much much shorter, and barely noticeable.
Thus, if I am try to take a series of pictures of a bird at high zoom, the camera will refocus between every two pictures, even if the subject is in focus to begin with.
I just tried on my old non-digital Rebel, and there no refocusing occurs if the subject is already in focus. Is this normal for the H1? Is it normal for all superzoom digital cameras?