Both v11 and v12 xspec use a conversion factor from keV to Angstrom of 12.39854. Using the current standard values of constants (CODATA(2002) via NIST) this factor should be 12.3984191. Apparently the difference is noticeable when plotting grating spectra in wavelengths. Made this change in both v11 (bug fix 11.3.2ac) and v12.
Keywords: HEAsoft, xspec