N=2 superfields and partial spontaneous breaking

We obtain a duality-transformed superfield form of the N=2 Maxwell effective holomorphic action with standard electric F1 term and demonstrate that in such a system off-shell N=2 supersymmetry is inevitably realized in unusual Goldstone mode corresponding to the partial spontaneous breaking down to N=1. In a system with the two sorts of F1 terms, off-shell N=2 supersymmetry is realized in partial breaking mode both in the electric and magnetic representations and this regime is retained on shell due to the Antoniadis-Partouche-Taylor mechanism. (author)