At line 726 in juce_ListBox.cpp I see this:
selectRow (jmin (totalItems - 1, jmax (0, lastRowSelected) + 1));
Problem is, when you display a ListBox with no selected rows and you press the down key,
the second row gets selected instead of the first one.
Did you by chance mean to write this instead?
selectRow (jmin (totalItems - 1, jmax (0, lastRowSelected + 1)));