[en] We present the analysis of Chandra X-ray Observatory observations of the eccentric γ-ray binary PSR B1259–63/LS 2883. The analysis shows that the extended X-ray feature seen in previous observations is still moving away from the binary with an average projected velocity of $\approx <!--\; ???\; -->0.07c$ and shows a hint of acceleration. The spectrum of the feature appears to be hard (photon index Γ ≈ 0.8) with no sign of softening compared to previously measured values. We interpret it as a clump of plasma ejected from the binary through the interaction of the pulsar with the decretion disk of the O-star around periastron passage. We suggest that the clump is moving in the unshocked relativistic pulsar wind (PW), which can accelerate the clump. Its X-ray emission can be interpreted as synchrotron radiation of the PW shocked by the collision with the clump.