From the Manual
ido-use-virtual-buffers is a variable defined in `ido.el'.
Its value is t
Original value was nil
If non-nil, refer to past buffers as well as existing ones.
Essentially it works as follows: Say you are visiting a file and
the buffer gets cleaned up by mignight.el. Later, you want to
switch to that buffer, but find it's no longer open. With
virtual buffers enabled, the buffer name stays in the buffer
list (using the `ido-virtual' face, and always at the end), and if
you select it, it opens the file back up again. This allows you
to think less about whether recently opened files are still open
or not. Most of the time you can quit Emacs, restart, and then
switch to a file buffer that was previously open as if it still
This feature relies upon the `recentf' package, which will be
enabled if this variable is configured to a non-nil value.
my ido settings are currently:-
'(ido-create-new-buffer (quote never))
'(ido-use-filename-at-point (quote guess))