  We analyze the solution of the Schr\"odinger equation arising in the
treatment of a geometric model introduced to explain the origin of the observed
shallow levels in semiconductors threaded by a dislocation density. We show
(contrary to what the authors claimed) that the model does not support bound
states for any chosen set of model parameters. Assuming a fictitious motion in
the $x-y$ plane there are bound states provided that $k\neq 0$ and not only for
$k>0$ as the authors believed. The truncation condition proposed by the authors
yields only one particular energy for a given value of a chosen model parameter
and misses all the others (conditionally solvable problem)
