Sometimes (typically on error) fylesystem size can be smaller that
partition size.
There is example:

1. I have disk:
   system      - 6Gb  - ext4 - /dev/sda1
   unformatted - 53Gb
   home        - 83Gb - ext3 - /dev/sda5
   swap        - 7Gb  - swap - /dev/sda6
2. I want to resize system disk to 59Gb (first and second unformatted
partition)
3. I reboot and load from CD. Run fdisk. Delete first partition (system
6Gb) and
   create new one (system 59Gb). Now my disk partitions:
   system      - 59Gb - ext4 - /dev/sda1
   home        - 83Gb - ext3 - /dev/sda5
   swap        - 7Gb  - swap - /dev/sda6
4. I rebbot and load normally. Run gparted. It`s show:
   system      - 59Gb - ext4 - /dev/sda1
   home        - 83Gb - ext3 - /dev/sda5
   swap        - 7Gb  - swap - /dev/sda6

   but then I run `df -h` and see:
   /dev/sda1              6,5G  5,6G   574M  91% /

   Filesystem on /dev/sda1 have old size. But gparted not show this!
5. Then I reeboot as su and run `resize2fs /dev/sda1`.
   Filesystem on /dev/sda1 become 59Gb (`df -h` show this).
   All ok.

-- System Information:
Debian Release: squeeze/sid
  APT prefers testing
  APT policy: (990, 'testing'), (500, 'unstable'), (500, 'stable'), (1,
'experimental')
Architecture: amd64 (x86_64)

Kernel: Linux 2.6.30-1-amd64 (SMP w/2 CPU cores)
Locale: LANG=ru_RU.UTF-8, LC_CTYPE=ru_RU.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/bash

Versions of packages gparted depends on:
ii  libc6             2.10.2-6               Embedded GNU C Library:
Shared lib
ii  libgcc1           1:4.4.2-9              GCC support library
ii  libglib2.0-0      2.22.4-1               The GLib library of C routines
ii  libglibmm-2.4-1c2 2.22.1-2               C++ wrapper for the GLib
toolkit (
ii  libgtk2.0-0       2.18.6-1               The GTK+ graphical user
interface
ii  libgtkmm-2.4-1c2a 1:2.18.2-1             C++ wrappers for GTK+ 2.4
(shared
ii  libpangomm-1.4-1  2.26.0-1               C++ Wrapper for pango
(shared libr
ii  libparted1.8-12   1.8.8.git.2009.07.19-5 The GNU Parted disk
partitioning s
ii  libsigc++-2.0-0c2 2.2.4.2-1              type-safe Signal Framework
for C++
ii  libstdc++6        4.4.2-9                The GNU Standard C++ Library v3

Versions of packages gparted recommends:
ii  gksu                          2.0.2-2+b1 graphical frontend to su

Versions of packages gparted suggests:
pn  dmraid                   <none>          (no description available)
ii  dmsetup                  2:1.02.39-1     The Linux Kernel Device
Mapper use
ii  dosfstools               3.0.9-1         utilities for making and
checking
pn  jfsutils                 <none>          (no description available)
pn  kpartx                   <none>          (no description available)
ii  ntfsprogs                2.0.0-1+b1      tools for doing neat things
in NTF
pn  reiser4progs             <none>          (no description available)
pn  reiserfsprogs            <none>          (no description available)
pn  xfsprogs                 <none>          (no description available)
ii  yelp                     2.28.0+webkit-2 Help browser for GNOME

-- no debconf information

In Debian: http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=572194