Stress/strain concentration in shear loadings

[feynman1]

A rectangle (plane strain/stress) is sheared on 3 edges (bottom fixed) so that it becomes a parallelogram. In theory this is pure shear and should undergo uniform deformation throughout the domain. The FEA result for this pure shear loading still shows stress/strain concentration on the bottom corners. Is that normal and how to get rid of them?

 

[Arjan82]

These corners are singularities

 

[feynman1]

These corners are singularities

Why should there be such singularities only on the bottom? In theory (uniform solution) the bottom corners aren't any different from the other 2 vertices. The fixed bottom is just the FEA boundary condition to prevent rigid body motions.