Comment 14 for bug 257790

My best guess as to the reason for this bug is that the kernel identifies some disks as "SEMB devices", whatever those are. See drivers/ata/libata-core.c, function ata_dev_classify (line 1082 in 2.6.27):

        if ((tf->lbam == 0x3c) && (tf->lbah == 0xc3)) {
                printk(KERN_INFO "ata: SEMB device ignored (lbam=0x%lx lbah=0x%lx\n", (unsigned long) tf->lbam, (unsigned long) tf->lbah);
                return ATA_DEV_SEMB_UNSUP; /* not yet */
        }

I modified the printk to report the values (as shown above), and got the values lbam=0x3c and lbah=0xc3. I have no idea what those mean, but maybe they're helpful.