Reeds warp. It's just the nature of the beast and not really worth getting too worried about. All it means is that the moisture content isn't equal in the veins and areas between them. If you don't know what the 'veins' are, hold a reed up to the light. They're the darker vertical lines/fibers.
If the reed is a good player you can flatten the back to take care of any warpage that may be happening there. A pocket knife, razor blade or piece of sandpaper on glass will do the job quickly and easily.
If the tip is getting a little wavy just soak it in some water or in your mouth for a couple of minutes, lay it on a flat surface or the table of your mouthpiece, and 'iron' out the wrinkles with your thumb by pressing from the heart to the tip a few times.
Slap it on and away you go.