  Bound entanglement, in contrast to free entanglement, cannot be distilled
into maximally entangled states by two local observers applying measurements
and utilizing classical communication. In this paper we ask whether a
relativistic observer classifies states according to being separable, bound or
free entangled in the same manner as an unboosted observer. Surprisingly, this
turns out not to be the case. And that even if the system in a given inertial
frame of reference is separable with respect to the partition momenta versus
spins. In detail, we show that if the spin state is initially bound entangled,
some boosted observers observe their spin states to be either bound entangled,
separable or free entangled. This also explains why a general measure of the
entanglement property is difficult to find.
