can't shrink an ext2 partition - what gives?

[Floydsmith]

e2fsck /dev/hda4
e2fsck 1.38 (30-Jun-2005)
/: clean, 59002/397312 files, 1264604/1582402 blocksa

Then run parted /dev/hda
Using /dev/hda
(parted) u kb
(parted) p
Disk geometry for /dev/hda: 0kB - 20020396kB
Disk label type: msdos
Number  Start   End     Size    Type      File system  Flags
1       32kB    8126576kB 8126544kB primary   fat32        boot
2       8126577kB 8398010kB 271434kB primary   linux-swap
4       8398011kB 10018391kB 1620380kB primary   ext2
3       10298051kB 15389498kB 5091448kB extended               lba
5       11893787kB 13464783kB 1570996kB logical   ext2
(parted) resize 4 8398011kB 10971491kb
Error: File system has an incompatible feature enabled.
(parted)
(parted) check 4
Error: File system has an incompatible feature enabled.
(parted)

What feature is this - how do I get rid of it?

floyd,