Yes, that is an undocumented "feature" of the new firmware.
Look here http://forums.dlink.com/index.php?topic=51588.0
Unfortunatelly, you can't downgrade back to v2.00, but try flashing v2.02 firmware, it will help you 
Thanks. I flashed the firmware to v2.02 and shortly after the reboot, I was getting 20MBps (give or take) on the ftp download of that ISO file. I couldn't test the ftp upload speed because it says "553 Users may not upload files". Not a big deal, as I am using ftp mainly for testing. I did a drag and drop of the file via the Windows share (though not via a mapped drive), and got about 10MBps both ways.
Unfortunately, about an hour later, when I tested the ftp download again, it was under 10MBps.
ftp> get ubcd511.iso
200 PORT command successful
150-Connecting to port 53314
150 368424.0 kbytes to download
226-File successfully transferred
226 37.687 seconds (measured here), 9.55 Mbytes per second
ftp: 377266176 bytes received in 37.68Seconds 10011.31Kbytes/sec.
ftp> get ubcd511.iso
200 PORT command successful
150-Connecting to port 53382
150 368424.0 kbytes to download
226-File successfully transferred
226 42.439 seconds (measured here), 8.48 Mbytes per second
ftp: 377266176 bytes received in 42.44Seconds 8890.24Kbytes/sec.
ftp> put ubcd511.iso
200 PORT command successful
553 Users may not upload files
ftp> quit