A strong ITB was sustained in a reversed shear discharge in JET during a long time interval after a significant reduction in plasma heating power. The observed ITB evolution is reminiscent of the effect of hysteresis. The mechanism of ITB sustainement was analysed. Modelling of the plasma heating and current profile were done using the TRANSP and JETTO transport codes. The resulting q-profile evolution was verified by comparison with the pitch angle d = Bp/Bt deduced from Motional Stark Effect (MSE) measurements (where Bp and Bt are poloidal and toroidal magnetic field, respectively). Turbulence stability was analysed using the gyro-kinetic code Kinezero. It was shown that strong negative magnetic shear produced by LHCD and sustained mainly by the bootstrap current in the plasma core is responsible for the turbulence stabilisation. Stabilisation due to shear of the plasma rotation and finite b-stabilisation play a complimentary role. The effect of bootstrap and LH driven currents on magnetic shear in JET discharges was analysed.