What causes one front side or the other to rise up when the steering wheel is turned?

 

The steering knuckes don't turn on a perfectly vertical plane, they are actually tilted rearward slightly. This is done so that the wheels return to the center when driving. Most vehicles are like this, but its usually more pronounced on trucks.

 

So when the wheels are turned (lock to lock) the leading tire(outer tire in a turn) dips slightly and the trailing tire(inner tire) rises slightly.

 

I think you hit the nail on the head. Excellant diagnosis. Didn't realize "caster" was the cause. Makes sense tho'.
Thanks very much. I'll not be concerned about it in the future.