We investigate the substituted spinel Mg 1 - x Mn 2 + x O 4 , in five powder compositions 0=<x=<1, where divalent Mg is expected to occupy mainly the B spinel site. A zero-field precession is detected for all samples below an x-dependent ordering temperature, which is different from that detected by macroscopic magnetization. The precessing amplitude in the ordered phase displays temperature-dependent deviations from the canonical value of 23, expected for our powder samples, indicating the presence of a radical state. The difference between the SQUID and the μSR-order temperatures is attributed to a collinear intermediate state stabilized by Mg.