Riks analysis in ABAQUS

I have been trying to analyse plate buckling by using Static Riks method in abaqus and I have been getting load factors greater than 1 at bifurcation. I have frist carried out the linear perturbation, buckling analysis and I am using its igen modes to introduce imperfections to the non-linear model. I have also defined self contact. Can someone tell me what would be the reason to get higher buckling loads for the non linear case?