Here is the problem. If you dynamically place controls in a panel, it works fine, but only until the vertical scrollbar appears. Once there is enough content for this to happen, it starts positioning controls nonsensically.
In my window, you can click a button to add another row of controls inside the panel, which represent options for an item in a list. If you scroll the vertical scrollbar on the panel all the way down and click the button again, the new row of controls will be positioned below the bottom edge of the panel out of view. If you scroll down, there is a huge gap between the new row and the previous row of controls. This should not happen. The positioning code is working flawlessly, as proven by debug output. As far as I can tell, the problem is the stupid anchoring system, however disabling anchoring on these controls does not fix the problem as one might expect. Instead, it just makes it position them wrong in a different manner. This makes no sense at all, and is super annoying!
I tried disabling Autoscroll in code before controls are added to the panel. No change. So I modified that code to disable both the vertical scroll bar and Autoscroll and set the scrollbar to not visible before controls are added. No change again, except that the now disabled vertical scrollbar still manages to appear usable when there is enough content in the panel in spite of it being disabled and set not visible!? That's not supposed to happen when I disabled and made it invisible! With anchoring disabled on the controls being added to the panel and once the vertical scrollbar has appeared, clicking the button to add a few more rows of controls now causes them to be indented a bit for no reason and positioned overlapping each other a bit vertically! It's as if the coordinate system in the panel has somehow arbitrarily changed, because of the presence of a vertical scrollbar and anchoring being disabled on the controls? The debug code shows that the controls are all being placed at correct coordinates, yet they appear positioned very wrongly. So my code is working perfectly, and therefore something else is the problem here.
Everything behaves exactly as expected up until the vertical scrollbar appears. This is so bizarre. Does anyone have any idea what on earth is going on with this stuff? Apparently it is far easier to make it do stupid stuff than to get it working properly.
Thanks again! I got it working. I went with TaW's solution first since it seemed like the simplest solution. Incidentally, I already tried TaW's approach days ago when I was fighting with it, but I had naturally subtracted the AutoScrollPosition value rather than add it, because I didn't expect it to be a negative value!
It seems very odd that control positioning is relative to the current AutoScrollPosition, as absolute coordinates seems like a much more natural, intuitive approach than having negative numbers. I guess that would make it slightly harder to place a control in the currently visible area, but I suppose that's not a big deal as most scrollable interfaces are probably initialized ahead of time and don't need to do that anyway.