HF10 zoom goes without any explicit request
My HF10 started to mysteriously autozoom as well, and I had made no setup changes. I don't have exactly the same symptoms as you describe except that it would begin to zoom when I didn't want it to. I noticed the [I.AF] (Instant AutoFocus) icon, so I went into the menu (Camera Setup - AF Mode) and turned the "Instant AF" to "Normal AF". After that, the autozoom seemed to have stopped. I set it back to "Instant AF" and it did not autozoom again. I wouldn't know how to turn the autozoom back on again even if I wanted to, but thankfully it appears to be gone now. Hopefully it will stay in manual zoom mode. Hope that helps.