Direct3D buffer problems

I am using Direct3D v9 in a cad application. I have discovered the following buffer problems: 1. I found that at start up, I must clear and present the back buffer (uses swap effect copy in a windowed MFC app) or an image from the last time I ran the app will be displayed on the screen. 2. Primitive creation is handled by a series of writes (Present()) to the graphics window. These writes will typically change the color of the primitive. The calls all appear to work. However, the displayed image does not reflect what should be on the screen. I know this because I captured the back buffer image to a bitmap before it was presented. The screen image does not match the last captured bitmap. Could this be a case of I/O blocking? I''m at a loss as to why the last Present() call does not display correctly on the screen. Any help would be greatly appreciated. Gort...Klaatu, Barada Nikto!