I'm baffled. 

I'm running through nightmare on the campaign,  I've defeated the first 7 sets of stages with my deliana/brogni duo, for 3 stars on each stage. 

But i get to the final stage of valdemar strait,  and despite again not losing either deliana,  it only gives me 2 stars.  I've run it 3 times.  2 stars every time. 

Why???