Anomalous transient tail diffusion is interpreted as being associated with the equilibration of the metastable state formed by the implantation process. During annealing, the sample approaches the thermodynamic equilibrium via quasi-chemical reactions involving radiation defects. The corresponding set of reaction-diffusion equations can be solved giving the space and time evolution of the defect profiles as well as their electrical activity. To exemplify the approach, the tail diffusion of the boron implants with peak concentrations transcending the solubility limit will be discussed in detail. Finally, a simple explanation will be given of the influence of lattice damage on boron diffusion due to pre- or post-implantation of silicon and boron atoms, respectively.