When I load a full
screen program on the primary display the secondary display
immediately goes into power save mode.

This will happen if you are in Horizontal Span mode.

I didn't have this behavior and could see and
use the secondary display regardless of the type of window that was
being used on the primary display.

This will happen if you're in DualView mode.

Please note that 3D performance will take a pretty big hit in DualView
mode, from my experience at least.