Nez.UI SetScrollBarPositions does opposite of parameter name.

[lllKXlll]

public ScrollPane SetScrollBarPositions(bool bottom, bool right)
{
_hScrollOnBottom = bottom;
_vScrollOnRight = right;
return this;
}

_hScrollOnBottom is doing the opposite of what's implied when set to True, putting the horizontal scrollbar on TOP of the scrollpane.
A quick fix would be to simply rename it to _hScrollOnTop.