sorry not to have got back to you sooner. Pre-conference chaos here...
It seems strange that the option isn`t appearing. At first I thought it could be an issue with tolerances (have you tried "double tolerances" in the Settings?).
However, the more I delve into this, the stranger it seems. At first I was able to recreate this error with my own PDSD/NCACX spectra. When trying with proton spectra everything was as expected. But when I then went back to the carbon spectra, I could no longer re-create the problem. Aargh! All I did was close the project and open another. Perhaps that will help you, too?
Will continue to try and work out what is going on here...