Currently, a ScrollViewer's contents can be navigated either by scrolling up/down with the mouse, or alternately, with Focus set on the Item Collection within, it can also be navigated using the Keyboard's ArrowKeys.

However, whilst a manual scrolling always succeeds in revealing the entirety of the first and last item in the list, using the ArrowKeys on the Keyboard appears to not succeed in display the entirey of the very first, and the very last Item in the list of Items.

See attached video.

At first glance in this example, this issue appears to related to the TreeView having a FixedHeight, inside of a ViewBox. I'm uncertain about this, but this is just the particular setup where I have been able to reproduce it 100% of the time. Otherwise, this appears to potentially be related to the 'MakeVisible' code.

This originally was discovered via this report: https://www.noesisengine.com/forums/viewtopic.php?t=3928

Repro Steps:

1) Download, unzip, and open the attached Project in Studio.

2) Play the Page, and use the Scrollbar, or the MouseWheel to move up and down the list to the very top, and very bottom extremities.
Observe how the first Item, and the last Item in the list are fully revealed at the top and bottom of the Scroll, respectively.

3) Set Keyboard Focus on an item in the list, if not already done. Then, use the up/down ArrowKeys to scroll to the very top, then to the very bottom of the list.
Observe how the first item, and the last item in the list, are cut-off at the top and bottom respectively.

Expected Results: Using Keyboard navigation in a ScrollViewer of items, reveals the entirety of all focused items within.