Annoying GD problem (imagecopy) ---- SOMEONE PLEASE HELP!!!!!!

I have two images, for the sake of clarity, call them image A and image B. Image B is smaller than A, and it has a yellow background with a black foreground. Image A is just a color image, nothing special. When I use imagecopy() and put B on top of A, image B loses its yellow background. Both are jpeg images, and I'm outputting them as jpegs. If I don't use imagecopy() and output the images after reading them, they remain intact. What's going on? Thanks for the help!