Attached you can find my screenshot.
I used for all the expansion the same report and made the drill-down on row PARENTH1_A.
(the original expansion for row is SELF,ALL AND TECH<>"Y",PARENTAFTER
Case A:
Original Formula Z23=X23-Y23
Original Formula AD23=AB23-AC23
File
screen3.PNG ----> report before drill-down Formula bar on Z23
screen4.PNG ----> report after drill-down Formula on Z23
screen5.PNG ----> report after drill-down Formula on AD23
Case B:
Changed formula Z23=SUM(X23)-SUM(Y23)
Changed formula AD23=SUM(AB23)-SUM(AB23)
File
screen.PNG ----> report before drill-down Formula bar on Z23
screen1.PNG ----> report after drill-down Formula on Z23
screen2.PNG ----> report after drill-down Formula on AD23
I also tried to use the working original formula form cell AD23 on Z23 and after the drill down the formula doesn't change ( file: screen10.PNG)