The aim of this note is to address the low energy limit of quantum field
theories with a minimal length scale. The essential feature of these models is
that the minimal length acts as a regulator in the asymptotic high energy limit
which is incorporated through an infinite series of higher order derivatives.
If one investigates a perturbative expansion in inverse powers of the Planck
mass, one generically obtains extra poles in the propagator, and instabilities
connected with the higher order derivative Lagrangian, that are however
artifacts of truncating the series