XSPEC and Chandra grating spectra

I have recently become aware (thanks to Lijun Gou and Mike Nowak) that the Chandra HETG ARF files include an EXPOSURE keyword which may differ from that in the spectrum (PHA2) file. If you are using XSPEC to analyze these spectra you should check whether the EXPOSURE values differ and if so replace that in the PHA2 file with the value from the ARF. The difference should only be significant if CC-mode was used.