We present the details of an accurate lifetime measurement of the 1 s2 2 s2 2p P 3/2 o2 metastable level in boronlike Ar XIV performed at the Heidelberg electron beam ion trap [A. Lapierre, Phys. Rev. Lett. 95, 183001 (2005)]. The lifetime was inferred from decay curves resulting from deexcitation of the metastable level to its P 1/2 o2 ground state through a magnetic-dipole (M1) transition upon cyclically turning on and off the electron beam. The measured lifetime of 9.573 (4) (+12 -5) ms (stat)(syst) is in disagreement with a trend of theoretical predictions of 9.53 (1) ms, which include the effect of the electron anomalous magnetic moment. Systematic effects were investigated by studying with high statistical significance the dependence of the decay times of the curves on various trapping conditions. The asymptotic trend of the decay times observed for increasingly high trapping potentials, which indicates negligible ion losses within a ms time scale, is in agreement with a theoretical model describing the ion escape rate in electrostatic ion traps. However, for high trapping potentials, we observed an unexpected slowly decaying component suggesting the presence of trapped low-energy electrons. Their origin, dynamics, and temperature, as well as their possible effects on the measured lifetime were investigated.