Air in the 1 lbs, 4 lbs and 8 lbs containers has moisture in it. All air contains water vapor. When you drop the tempature of the area that the container is in, it forms ice cristals. This is general indicated as freezer burn. When taken out and brought to room tempature it turns back first to liquid water and then depening on the tempature back into vapor.
What effect this has on powder and primers, I can not say, but it certianly is not good on concrete, rocks or any other solid objects.
If you read the instructions on the containers of powder, it says to store in a "COOL, DRY PLACE", not a "COLD, DRY PLACE".