I just installed kernel 2.4.20 ( wich is the same as 2.4.20rc-4 ) a couple of days ago and now I read
this piece about a bug in the final 2.4.20 kernel..

source: this article

In 2.4.20-pre5 an optimisation was made to the ext3 fsync function
which can very easily cause file data corruption at unmount time. This
was first reported by Nick Piggin on November 29th (one day after 2.4.20 was
released, and three months after the bug was merged. Unfortunate timing)

This only affects filesystems which were mounted with the `data=journal'
option. Or files which are operating under `chattr -j'. So most people
are unaffected. The problem is not present in 2.5 kernels.
Luckily now there is also a patch available ! !