We investigate quantum corrections to the primordial fluctuations in the single-field inflationary paradigm from spectator fields that experience a smooth transition of their vacuum expectation values. We show that when the phase transition involves a classical evolution effectively driven by a negative mass term from the potential, important corrections to the curvature perturbation can be generated by field perturbations that are frozen outside the horizon by the time of the growing phase. At one-loop level, the dominant channel for the production of primordial fluctuations comes from a pair-scattering of free spectator fields, different from the usual conclusion for massive fields that always stay in one stable vacuum state.