I've created a simple program using DX9 in windowed mode. It uses a simple diffuse shader to render a mesh in a 640x480 window. The program seems to work fine but there's a strange array of stretched pixels which distort the image. Here's a shot:
If you can't see them, here's the same image after edge-detect:
Is there anything I'm overlooking that needs to be done to render in windowed mode (I've been doing fullscreen stuff until now). Thanks!