  We present results of magnetic measurements relating to vortex phase diagram
in a single crystal of FeSe$_{0.5}$Te$_{0.5}$ which displays second
magnetization peak anomaly for $H \parallel c$. The possible role of the
crystalline anisotropy on vortex pinning is explored via magnetic torque
magnetometry. We present evidence in favor of pinning related to spatial
variations of the charge carrier mean free path leading to small bundle vortex
pinning by randomly distributed (weak) pinning centers for both $H \parallel c$
and $H \perp c$. This is further corroborated using magnetization data for $H
\parallel c$ in a single crystal of FeSe$_{0.35}$Te$_{0.65}$. Dynamical
response across second magnetization peak (SMP) anomaly in
FeSe$_{0.5}$Te$_{0.5}$ has been compared with that across the well researched
phenomenon of peak effect (PE) in a single crystal of CeRu$_2$.
