samba - Feb 2007 - Serious: corrupt file content using FlashGet

I am using FlashGet (download manager, segmented downloads) to download
files via http to a samba drive. I found that the downloaded file is
largely corrupt and contains chunks of zero bytes (instead of downloaded
bytes).

Samba version is 3.0.24. Linux is Gentoo. Kernel is vanilla 2.6.19.2.
Filesystem is XFS.

On ext3 corruptions occur, too. However I found fewer zero byte areas.

Any ideas?