Fellows, I am not saying that you haven't had problems with the track 'moving' on you, but to say a short (or long) section of rail expands and contracts 1" is a bit much for any type of metal. It doesn't take but about 1/32" too long for one side of a joint to considerably bow the the other side.
The last several years I have read of many problems with laid track walking or becoming misaligned and discussions of what environmental conditions are causing this. No one seems to agree and no one geographical area seems to have more than the other.
As a reply to what all you have said, my layout is in a garage that is separate from the house. It is only heated or cooled when I plan on working or operating in it. I have over 1,000 feet of Atlas Flex, soldered at each joint, ballasted only in viewed areas, and nailed about every other hole. I live in an area of very high humidity in the state of Alabama. My present layout is 3.5 years old and built with prime lumber and BC plywood. Maybe it is luck, but I do not and have not experienced any problems associated with the environment.
My personal opinion, is that the "track alignment" is not so much of the tracks expansion/contraction, but the benchwork itself. Remember that the frame and top are all mechanically fitted together in a way that each member supports or assist the other. So, if one area is stressed by the environment or other influences, then the whole section or area will try to adjust for the change.
I also believe that a lack of humidity is more responsible for the track alignment problems experienced by so many, than too much or from temperature variations. If your layout is in a dry area, then you should always season your lumber until it's moisture content will equal out with the average humidity in the layout room. If this is not done, then the drying effects will certainly cause warping regardless of the grade of lumber. Also and after the layout is built, you should try to maintain a steady humidity and temperature level.
If your area (such as mine) has higher humidity, then the chances of the lumber warping are less severe unless you make drastic and fluctuating changes to the ambient air. Still, care must be made to ensure that you have secured the parts of your benchwork properly with the use of many screws and supports, as the lumber will still dry a little more than when you bought it. The use of many screws where a few would do the job, will help keep the bench parts in place to the measurements that you built.
Please keep in mind that the above is my opinion and is not meant to be argumentative, but is posted to give another view in a positive way.