  We consider the singularities of the zero temperature renormalization group
flow for random elastic manifolds. When starting from small scales, this flow
goes through two particular points $l^{*}$ and $l_{c}$, where the average value
of the random squared potential $<U^{2}>$ turnes negative ($l^{*}$) and where
the fourth derivative of the potential correlator becomes infinite at the
origin ($l_{c}$). The latter point sets the scale where simple perturbation
theory breaks down as a consequence of the competition between many metastable
states. We show that under physically well defined circumstances $l_{c}<l^{*}$
and thus the apparent renormalization of $<U^{2}>$ to negative values does not
take place.
