turns out the canned new "backup directory" dialog put its "back" and
"next" buttons at a different relative horizontal position than all the
other canned dialogs.  This explains why you had to keep moving the
mouse around if you wanted to do a straight all-default install -- the
Next button kept moving around.  Now the back/next buttons are in exactly
the same place on all dialogs, and you can click straight thru to the end.