{DDSCAPS_TEXTURE | DDSCAPS_3DDEVICE, DDSCAPS2_TEXTUREMANAGE, DD_OK,
DDSCAPS_SYSTEMMEMORY | DDSCAPS_TEXTURE | DDSCAPS_3DDEVICE,
DDSCAPS2_TEXTUREMANAGE },
What happens if you try to create a device on such a surface or assign it as a render target for an existing device?
I expect the answer to be somewhere between "driver dependent error code" and "BSOD", but it would be good to check.