  Nonlocal nature apparently shown in entanglement is one of the most striking
features of quantum theory. We examine the locality assumption in Bell-type
proofs for entangled qubits, i.e. the outcome of a qubit at one end is
independent of the basis choice at the other end. It has recently been claimed
that in order to properly incorporate the phenomenon of self-observation, the
Heisenberg picture with time going backwards provides a consistent description.
We show that, if this claim holds true, the assumption in nonlocality proofs
that basis choices at two ends are independent of each other may no longer be
true, and may pose a threat to the validity of Bell-type proofs.
