For what it is worth... I am starting to understand the zoom behavior in FCPX... moreover, I like it. I am so accustomed to the legacy zoom behavior in FCP Studio that I didn't consider that it might work differently in FCPX, I just thought it was broken in FCPX.
Basically, the zoom function doesn't care where the playhead is at all. It cares where your cursor is hovering above the timeline. Note that you have two vertical lines in your timeline. One is the playhead, the other is the location of your cursor. When you zoom in, the cursor location is where the zoom is centered. So if you move your cursor over your playhead, then zoom, you are zooming to the playhead.
This is perfectly acceptable behavior that allows you to instantly zoom to any location in your timeline simply by hovering your cursor there before zooming.
Hopefully this helps.
Matt