Dynamical NNLO parton distributions and the perturbative stability of F_L(x,Q^2)

It is shown that the previously noted extreme perturbative NNLO/NLO instability of the longitudinal structure function F_L(x,Q^2) is a mere artefact of the commonly utilized `standard’ gluon distributions. In particular it is demonstrated that using the appropriate – dynamically generated – parton distributions at NLO and NNLO, F_L(x,Q^2) turns out to be perturbatively rather stable already for Q^2 $\ge$ O(2-3 GeV^2).