Anomalous behaviour of the complex dielectric constant ε* at Tt was revealed in thermally depoled samples of PLZT X/65/35 ferroelectric ceramics with X = 9.25 and 10 by means of infra-low-frequency dielectric spectroscopy in ultra-weak fields (E∼ = 0.1 V/cm). It was observed that the value of the additional maximum ε' in the Tt region increased for diminishing measuring field frequencies and tended to drift towards lower temperatures. The frequency-temperature dependence ε* of samples affected by biasing electric fields was investigated. The emergence and evolution of polar regions in the ferroelectric ceramics in a quasipolar phase was investigated by measuring the light depolarisation due to the longitudinal effect of light scattering.