That is exactly what is being shown here John. It was a theory they were working on in the ninetys. Never really worked. Was this down the center wall of the home??
Here is my verbage for truss uplift.
Cracks were noted at the wall/ceiling intersection and appear to be from truss uplift. The following explains the issue:
Houses have changed over the years. Attics of newer houses have lots of insulation and ventilation. They also have roof trusses instead of rafters and ceiling joists.
The bottom chord of a truss is buried below a deep blanket of insulation. Even on the coldest days the bottom chord is nice and warm. The top chords however, are above the insulation and get very cold in a well ventilated attic.
While the bottom chord is warm and is drying out, the top chords are doing just the opposite. The cold winter air has very high relative humidity. The top chords absorb moisture from the air causing them to elongate.
With the top chords growing and the bottom chord shrinking, the truss arches up in the middle causing the ceilings to lift off the walls. In the summer, the cycle reverses itself.
This is not considered a structual defect but mother nature at work. You may wish to install a molding (in winter)to hide the crack or a small amount of paintable caulking may help.