I'm building a dashboard where a user selects a dropdown item that has the value of a search macro name and then a single value panel is rendered as a stats dc(X) (where X is a named field found in both macros).
However, I'm running into a strange occurrence where if I select a macro to set diff against itself, the value isn't 0,
Because you are using subsearches which have both time, size and memory available limits, which may be hit at different places for different runs of the same search. There are MUCH better ways to do diffs than set diff and I always use those other ways. I have never had to use set diff to get the job done.