  By scaling isothermal magnetization data measured at different temperatures
in the mixed state of high-Tc superconductors, we show that in some cases the
sample magnetization, measured in increasing magnetic field below the
irreversibility line, is identical with the equilibrium magnetization even in
magnetic fields well within the irreversible regime. This surprising behavior
can hardly be explained in terms of traditional models of vortex pinning in the
bulk of the sample.
