One thing that is confusing to me is that I was thinking of the mash profiles being static, stand-alone settings in the profiles->mash area. However, they seem to be dynamic in that if you have a recipe that uses an equipment profile that has a mashtun with a nonzero deadspace loss value, the mash profile used in that recipe shows the corresponding deadspace value. And if you have a different recipe that uses an equipment profile that has a mashtun deadspace loss of zero, the mash profile does not display the deadspace value. I guess that makes sense, but the change to the mash profile settings file without my knowledge caught me by surprise. I hope I'm understanding this behavior correctly.
Long ago I made a conscious effort to duplicate the default temperature mash profiles which seem to be fashioned for a brew pot with no deadspace and named them for my system which definitely has a mash tun deadspace. Not sure if this was the right thing to do, but none of the default profiles display the deadspace field when I examine them in the Profiles->Mash area. Looking at my duplicated mash profiles, it's probable I have not used all of them in a recipe that uses my system's profile that has deadspace. Therefore, if I open one of those unused, duplicated profiles, it still has no association with my equipment profile, and as a result, does not show the deadspace field. I hope I have that right.