  Gauge symmetry breaking by boundary conditions is studied in a general warped
geometry in five dimensions. It has been suggested that a wider class of
boundary conditions is allowed by requiring only vanishing surface terms when
deriving the field equations for gauge theories on an interval (i.e., employing
a variational principle), in comparison to the twist in orbifolding with
automorphisms of the Lie algebra. We find that there are classes of boundary
conditions allowed by the variational principle which violate the
Ward-Takahashi identity and give four-point tree amplitudes that increase with
energy in channels that have not yet been explored, leading to cross sections
that increase as powers of the energy (which violates the tree level
unitarity). We also find that such boundary conditions are forbidden by the
requirement that the definitions of the restricted class of five-dimensional
(5D) gauge transformations be consistent.
