Strange corruption (?) problem

[Professor Stafylopaths]

Hello,

I seem to have a strange problem with an ext3 fs partition.
Whenever I transfer several files to this partition and compare
the md5 and sha1 sums with the originals don't match. Seems like
this takes place only with large files (~700MB). I am using vanilla
2.4.27 linux kernel (haven't seen any significant changelog entries
through the latest kernel that might be relevant to my problem).
I've also run e2fsck -C -v -c -f as well as on the partition which didn't
reveal any problems at all.
This partition was corrupted somehow in the past, but was completely
recovered by fsck, although probably it now makes use of a backup
superblock (when I try to mount the partition without any parameters
the kernel mounts it as ext2 with the warning "EXT2-fs warning (device
ide0(3,65)): ext2_read_super: mounting ext3 filesystem as ext2", so I always
specify the fs type by -t ext3 parameter). I don't know whether this is relevant
to the current problem.

Any ideas?