Anomalous paramagnetic effects in dc magnetization were observed in the mixed state of ${\mathrm{LuNi}}_{2}{\mathrm{B}}_{2}\mathrm{C}$, unlike any reported previously. It appears as a kink-like feature for $H$⩾${}30\phantom{\rule{0.3em}{0ex}}\mathrm{kOe}$ and becomes more prominent with increasing field. A specific heat anomaly at the corresponding temperature suggests that the magnetization anomaly is due to a true bulk transition. A magnetic flux transition from a square to an hexagonal lattice is consistent with the anomaly.