autocompletion fails to work entirely for some commands (e.g. mount)

In natty, if the type characters match a singe directory entry, pressing the TAB key results in the matching entry, with:
1: A space following
2: No escaping of embedded spaces or special characters

This is NOT related to unity - it appears for the classic desktop as well

In previous releases, bash would do the following:
1: For embedded spaces, they would be escaped with a single backslash ("\")
2: If the match was a directory, the displayed match would terminate with "/' (eg "Desktop/") and NO trailing space
3: A trailing space would be appended ONLY in the case where there was a single file name that matched when the TAB was pressed

bash version:

tim@zaphod:~$ bash --version
GNU bash, version 4.2.8(1)-release (x86_64-pc-linux-gnu)
Copyright (C) 2011 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>

This is free software; you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.
tim@zaphod:~$ lsb_release -a
LSB Version: core-2.0-amd64:core-2.0-noarch:core-3.0-amd64:core-3.0-noarch:core-3.1-amd64:core-3.1-noarch:core-3.2-amd64:core-3.2-noarch:core-4.0-amd64:core-4.0-noarch
Distributor ID: Ubuntu
Description: Ubuntu Natty (development branch)
Release: 11.04
Codename: natty
tim@zaphod:~$

Confirming originally reported behavior. Also see bug 769866 for other bash completion failures in natty, which include what @Tim Frost is talking about in comment 2.

Despite bug 769866 looking inexplicably fixed today, this is still not working on my system (yet still does work on lucid), using the "sudo mount" testcase. mount does work without sudo, though the command itself fails obviously (only root can do that). :-)

I'd like to point to the *original* poster's (i.e. Ngassam's) description of the issue. 769866 is not the same issue.

The issue at hand here is that some commands (e.g. the mount command) fail autocompletion when prefixed with sudo. Using "mount" as regular user will autocomplete on tabbing in order to find source device and mount target folder paths. Same applies if logged in as root. When prefixing "sudo" tab path autocompletion stops working.

This applies to Oneiric and Natty, in X sessions, TTYs and SSH. Not sure if it applied to Maverick -- AFAIR it didn't.

As the bug continues to exist with Precise, maybe it's time to actually assign this to someone, perhaps give it some importance? :)

FWIW, the fix is apparently quite trivial:

http://ubuntuforums.org/showthread.php?t=1769100