RGS spectra (stacked for visual purposes) from observation 0865440501 around the excluded 22.25–24 Å region. Two spectral models are shown, and the most important model features are denoted with labels. The green model includes the problematic region while the blue model ignores it. The green model clearly overpredicts the broadening of the medium-width O VIII and N VII features. The position of the possible instrumental feature is indicated by the arrow.