(written by Geert Uytterhoeven)
This bug apparently appeared in kernel 2.1.15. Geert says:
"Gadi Oxman (the IDE guru) told me this could be due to buggy IDE interfaces, IDE drives or both (or a bug in the driver, of course :-), and he suggested to try "ide0=noautotune" which solved my problem last Thursday. But I can't be 100% sure this really solved it..."
More recent work has apparently resolved a lot of the IDE bugs people were seeing; try kernel 2.1.119 or later and see if that will fix the problem.