Using an exact diagonalization technique, we calculate the distribution of electrons n(nu) over single-particle quantum states in few-electron parabolic quantum dots. We show that n(nu) is a function of quantum numbers nu, but not of the energy of the states E-nu, n(nu) not equal n(E-nu). The common property n(nu) = n(E-nu) remains valid only if electron-electron interaction is neglected. For certain cases in the strong interaction regime, the occupation numbers of higher-energy levels may be larger than those of the lower-energy states: n(nu) > n(nu ') at E-nu > E-nu '.