It's wood. It warps. Subjecting wood to extreme changes in temperature and humidity will increase your chances of warping, but their are other factors as well, such as stresses built into the lumber from the growth , sawing and storage. Even planing unevenly can cause warping.
One thing is clear: if the wood wants to bend, it bends.
Wood is like a sponge like material made of cells and fibres that swell and shrink depending on the temperature and moisture in the surrounding air, although to different extents in different directions. To minimize warping it is important to acclimate and store wood correctly.
How to Acclimate and Store Wood.
Keep the boards stacked on thin sticks between each one and not directly on a cement floor. Alternatively keep them stacked at an angle against a wall. Leave the boards to acclimate to the climate in your shop for up to a week before using.