  Here we consider the set of bundles $\{V_n\}_{n\geq 1}$ associated to the
plane trinomial curves $k[x,y,z]/(h)$. We prove that the Frobenius
semistability behaviour of the reduction mod $p$ of $V_n$ is a function of the
congruence class of $p$ modulo $2\lambda_h$ (an integer invariant associated to
$h$).
  As one of the consequences of this, we prove that if $V_n$ is semistable in
characteristic 0, then its reduction mod $p$ is strongly semistable, for $p$ in
a Zariski dense set of primes. Moreover, for any given finitely many such
semistable bundles $V_n$, there is a common Zariski dense set of such primes.
