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.
--
https://gitlab.winehq.org/wine/wine/-/merge_requests/2404#note_68109
Yet another four files with the same "issue": server/change.c, server/thread.c, server/process.c and server/queue.c. This time found by fgrep(1), so no more similar files left in server directory, I believe.
--
https://gitlab.winehq.org/wine/wine/-/merge_requests/5503#note_68027