Hiya.

Could you provide a test model for us to try? Or, if it's commercially bought, which and where (one of us may have it)?

First guess...the version of .x is to blame. So you could save a .x model for DX9, and when you went to open it in a DX7 app it would be screwed up. I believe A7 uses DX8...so a model other than a DX8 model in .x format may have issues. Does the DirectX Viewer app let you resave models into different DX versions? If so, try doing that for DX6 through DX9 (or maybe even DX10) and test each one.