What version of RattleCad? I'm using 3.5.14 and the only tabs that show stack and reach are the "frame drafting: and "frame details". Both tabs are in agreement on my version.

I don't concern myself with those numbers for designing a frame. They are just the result of placing the saddle, bars and bottom bracket where I want them with the stem length that I specify. To me, stack and reach are a means for consumers to compare two frames and not numbers to be used in designing a frame.