selection of articles using keyboard shift-up/down combination doesn't work
as expected if up/down arrow is pressed and released and then pressed again
while holding shift down.  it seems to only keep the current article and 1
or 2 previous articles selected as opposed to retaining the entire previous
selection.  however, if up/down arrow is held down instead of pressing and
releasing it, selection works as expected.

if shift is held down during pressing and releasing up/down arrow, one
would expect that previously selected items would remain selected as is the
case in the group pane.

also, this scenario doesn't work as expected:
1) select an article
2) hold shift down
3) press down (correctly selects fist and second articles)
4) press up

One would expect that this would cause the first article to remain selected
and the second deselected, but both remain selected.