It may be worth including a call to GetVertexBufferDesc() in the tests. As Matteo mentioned in an earlier comment, the docs seem to suggest that omitting D3DVBCAPS_SYSTEMMEMORY allows the driver/runtime to place the buffer as it sees fit.
I mentioned earlier that GetVertexBufferDesc() never returns anything other than the flags used to create the buffer. That holds for both cards. I'll add a test the the suite.
Actually, those tests are probably helpful separate from this bug as well; we don't seem to have a lot of test coverage for GetVertexBufferDesc()...