It is well known that activating one slip system increases the strength of other slip systems in metallic materials, a phenomenon known as latent hardening subjected to combined loadings. This hardening behavior can be understood by the “forest hardening” of dislocation interactions at the continuum scale. At sub-micron length scale, plastic deformation is known to be governed mainly by dislocation sources, instead of their mutual interactions. This is because as the size of the sample decreases, the interactions between dislocations become increasingly sparse. In our research, we examined two types of combined loading conditions in a single crystalline Cu micropillars: tension after torsion and torsion after tension. Comparing these combined loadings with simple tension and torsion, respectively, we found that there is a transition from latent hardening to “latent softening” as the size of the sample decreased, meaning that the dislocations would act as sources of plasticity. We can see that the dislocation behavior plays an important role in changing the governing mechanism from latent hardening to latent softening, depending on the sample size.