Yep, it's combined mode. The issue:
1. As of kernel 2.6.26 the combined_mode quirk is no longer supported.
2. hdX=none doesn't work, because the ata_piix driver thinks I don't have a SATA controller. (This is distinctly abnormal, and hasn't happened on any other Linux distro.)
3. I can't recompile the kernel.
4. I can't change the option in the BIOS, because I'm using a cheap Acer laptop with drives locked in IDE emulation mode.
So basically, unless issue #2 can be fixed, I'm SOL.