The investigation of the dynamic stability of solutions in positional games with the incomplete information has been carried out in the class of mixed strategies for n persons. The theorem about the strong dynamic stability of the E-equilibrium set in mixed strategies has been proved. The simplest positional game with two players has been considered which has shown the dynamic instability of the optimization principle. The similar exclusions should be taken into account at studying of the solution stability in different classes of n-person games using mixed strategies.