down-arrow usually only selects next message in the message list pane: it
wont fall off the end of the list and highlight the attachment button in
the message body, or the quicksearch text input box.

Clicking on the attachment button in the message body gives keyboard focus
to the message display. Down arrow now selects firstly the attachment
button itself, down arrow again then goes to the quicksearch text input
field, and next to the message list. It is now back to the "normal" mode of
only selecting messages and doesnt fall off the end, making it impossible
to select the attachment button and the search text this way even if I
wanted to.