One of the most striking feature is that the EW curve (Fig.) is the ``mirror'' image of the radial velocity curve (Fig.). Only the EW maximum between phases 0.74 and 0.83 is truncated with respect to that of the radial velocity curve. A similar correspondence for RR Lyrae was already observed by Chadid and Gillet (1997) with the BaII4934.076Å line which was first wrongly identified as FeI 4934.082Å. Some line profile modelling tests with our nonlinear nonadiabatic pulsating model show that this unusual behaviour, for this line, is due to the combination of excitations, ionizations and changes of atmospheric thermodynamic and hydrodynamic conditions within the line formation region. Indeed, depending of atomic properties of the considered line transition, the EW can increase when the atmosphere is expanding and decrease when it is compressing. Although, in general, there is not a well marked correlation between radial velocity and EW curves, here this was accidentally the case with the selected line.