  We argue that the non-adiabatic evolution of spin states in Stern-Gerlach
apparatus can blur the manifestation of path spin entanglement. This fact
introduces a contradiction to the usual perception of spin measurement even in
a formally ideal situation. Through quantitative calculation, we have pointed
out the specific reason behind the breakdown of adiabatic evolution to be the
spatial inhomogeneity of applied magnetic field. The angle $\theta$ between the
$z$ component of magnetic moment of the particle and applied magnetic field is
also a determining factor for the category of evolution of spin states.
Adiabaticity always can be restored by choosing a sufficiently small value of
$\theta$. Considering azimuthal inhomogeneity, we have examined the nature of
path spin entanglement in the context of Stern-Gerlach experiment.
