In microspecimens the dislocation microstructure evolution under fatigue loading is unusual: Bending experiments with single crystalline microbeams show the development of slip traces on the surfaces which are generated by dislocations leaving the specimen . Under load, the dislocations are pushed in and over the neutral plane of the gradient and stabilized in a pile-up . Upon unloading, the geometrically necessary dislocations disappear, but the dissolution path of the pile-up and the reason for associated permanent plastic deformation is less clear. By using Discrete Dislocation Dynamics simulations it is shown that the explanation for the formation of a slip trace during unloading and the almost dislocation free sample is an asymmetry between the backward and forward motion due to the mutual dislocation interaction . Additionally, the imperfect geometry (e.g. taper) of the sample can introduce a bias due to the geometrically imposed change in length of dislocations during glide . Based on this mechanism, the specimen can fail without storage of dislocations.