The so-called "intermediate" phase in lead zirconate (PbZrO3) is shown to exhibit a peculiar dielectric signature, both as a function of time and of frequency, on the contrary to the low temperature antiferroelectric and high temperature paraelectric phases. This signature is present over a temperature range that overlaps with the paraelectric phase and depends on whether the sample is cooled or heated. In addition, the time dependence of the dielectric constant indicates that PbZrO3 evolves isothermally toward a state that is neither the one measured while heating nor while cooling. We ascribe the observed non-ergodicity to the establishment of a modulated phase stabilized by polar defects. (C) 2014 AIP Publishing LLC.