Hi all, I'm building some doors out of African mahogany. I milled down the lumber for two doors...one set is perfectly fine, square, and stable, the other side cupped and/or warped so badly that its likely unusable for this project. It moved in both directions: it cupped along the wide front and also along the thin edge.

What causes this? Is there something intrinsic to the particular piece of lumber that caused it to 'release' when I started milling it, or did I screw up my milling process? Any advice on how to avoid this in the future?