Comment 49 for bug 38915

I'm having a similar problem (just like Muriloq described) but my system is not locking up or freezing. The shutdown process continues and the pc is successfully turned off.
The options quoted above do any good for me.
It might has something to do with Usplah, but I'm not sure.
If you are wondering, NO, this doesn't happen during the boot process. Go figure huh?!.

Here's my card description:
01:00.0 VGA compatible controller: Silicon Integrated Systems [SiS] 65x/M650/740 PCI/AGP VGA Display Adapter (prog-if 00 [VGA])
        Subsystem: Silicon Integrated Systems [SiS] 65x/M650/740 PCI/AGP VGA Display Adapter
        Control: I/O+ Mem+ BusMaster- SpecCycle- MemWINV- VGASnoop- ParErr- Stepping- SERR- FastB2B-
        Status: Cap+ 66MHz+ UDF- FastB2B+ ParErr- DEVSEL=medium >TAbort- <TAbort- <MAbort- >SERR- <PERR-
        BIST result: 00
        Region 0: Memory at c0000000 (32-bit, prefetchable) [size=128M]
        Region 1: Memory at cfee0000 (32-bit, non-prefetchable) [size=128K]
        Region 2: I/O ports at bc00 [size=128]

I also see the (error) message 'inappropriate ioctl for screen device'' during the shutdown.