Keni, with all due respect, I don't think you are taking advantage of what the tools offer. I just don't understand what you're trying to do that you think Sonar can't do, and I see nothing you've found that qualifies as a "bug." You most certainly can type Z, select an area, and whatever area you select (including a single track) will fill the whole track view, assuming that's what you want.
I'm not exactly sure what it is you want to accomplish, but I have a recommendation based on a workflow that works really well for me.
This is based primarily on auto-zoom, which is FANTASTIC once you get the hang of it. I often want to be able to see as many track headers as possible BUT also work on an individual, zoomed in track. This is easy with auto-zoom, and here's my workflow:
1. Hit Shift-Z to enter auto-zoom.
2. Select a track, THEN adjust the selected track's height by dragging on the splitter bar to the subjectively optimum viewing height (usually pretty high).
3. Any track header you click on will now expand to the optimum viewing height, and the previously selected track will collapse. Or (I do this a lot) use the up/down arrow keys to go to a different track. As you pass by a track, it will expand and then collapse after you go past...a convenient "preview" function.
4. The complement to this is I use ctrl right arrow and ctrl left arrow to zoom in and out horizontally.
(Note that this does NOT expand Take Lanes because
they are not tracks. They are for recording takes.)
I find this a really efficient way to zoom in to any degree I want on any track. But, there are a zillion different ways to zoom. All you need to do is find the one or two ways that work really well for you.
Rather than saying everything is "messed up," please describe exactly what it is you want to accomplish. I'm sure there are several ways to do pretty much anything you want when it comes to zooming.