Quadro FX 570 Back buffer not being erased

I am testing my graphics card with a program that allows per-frame control of what is rendered on screen. I suspect that the back buffer is not being cleared before the new scene is drawn to it. For example, the first frame may consist of a red square on screen, and the second and third frames a blue square offset from the red square by some amount. The first two frames are drawn correctly (red then blue), but the third frame includes the red square from the first frame with the blue square drawn over it. In other words, before drawing the blue square on the back buffer in preparation for the third frame, the red square that had been drawn there before was not erased.

I have drawn a similar sequence of shapes to screen with other video cards without issue. The failure to clear the back buffer before drawing the new scene only occurs with the Quadro FX 570. Is there some setting that can fix this? I have restored my video card's defaults and the problem persists.