The Gamow-Teller matrix elements of 2 nu beta beta transitions to a 2₁⁺ final excited state has been calculated within the QRPA formalism for ⁷⁶Ge and ¹³⁶Xe. The relative stability of the calculation with respect to the particle-particle interaction strength is confirmed; on the other hand, the results are strongly dependent on the choice of the single-particle energy levels. A plausible explanation of such behaviour, originating in the interference of the individual contributions due to the third power of the energy denominator, has been proposed.