Out of pure curiosity I have installed the BIOS update for my lifebook (version 131), and voilá, all of a sudden ACPI works.
You can download the BIOS update from the official Lifebook homepage. Please note however that the update is not listed for every model. When you choose model C-6185 for example, the download site will tell you that there are no updates available. The update itself however lists C-6185 as supported model. Choosing model C-6555 will lead you to the correct BIOS update.
Please keep in mind that a BIOS update may as well trash your laptop, so only update your BIOS if you know what you are doing and don't blame me if it fails.