  In loop quantum cosmology, ambiguities in the Hamiltonian constraint can
result in models with varying phenomenological predictions. In the homogeneous
isotropic models, these ambiguities were settled, and the improved dynamics was
found to be a unique and phenomenologically viable choice. This issue has
remained unsettled on the inclusion of anisotropies, and in the Bianchi-I model
there exist two generalizations of isotropic improved dynamics. In the first of
these, labelled as $\bar \mu$ quantization, the edge length of holonomies
depends on the inverse of the directional scale factor. This quantization has
been favored since it results in universal bounds on energy density and
anisotropic shear, and can be viably formulated for non-compact as well as
compact spatial manifolds. However, there exists an earlier quantization,
labelled as $\bar \mu'$ quantization, where edge lengths of holonomies depend
on the inverse of the square root of directional triads. This quantization is
also non-singular and so far believed to yield a consistent physical picture
for spatially compact manifolds. We examine the issue of the physical viability
of these quantizations for different types of matter in detail by performing a
large number of numerical simulations. Our analysis reveals certain limitations
which have so far remained unnoticed. We find that while being non-singular,
the $\bar \mu'$ quantization suffers from a surprising problem where one of the
triad components and associated polymerized term retains Planckian character
even at large volumes. As a result, not only is the anisotropic shear not
preserved across the bounce, which is most highlighted in the vacuum case, but
the universe can exhibit an unexpected cyclic evolution. These problematic
features are absent from the $\bar \mu$ quantization leaving it as the only
viable prescription for loop quantizing the Bianchi-I model.
