In the paper, a theoretical background of the unexpected third-order intermodulation power decrease at some levels of input power is discussed first. This anomaly can be partially explained by various physical phenomena, RF stress, e.g., as shown in the state-of-the-art review in the paper. Then a simulation of the IM3 dependency is performed, including a comparison between the computed and measured IP3 points. Finally the single- and double-band low-noise amplifiers designed by multi-objective optimization are measured from this point of view, and a frequency dependence of the IM3 anomalies is demonstrated. An improved optimization method is defined too.