  We identify a new regime of decay of the irreversible magnetization in clean
Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8}$ crystals, at induction values close to the
``second peak field'' at which the bulk critical current density steeply
increases. A time window is identified during which the decay of the induction
is controlled by the slow propagation of the phase transformation front across
the sample.
