Custom changes in GGB1 doesn't carry over or apply

So we created a customized logic successful GGB1 specifically successful exit U0001. Z_OBJECT calls the U0001. 

Since the ZOBJECT, I person created a logic for BSEG-FDTAG.

Initially, the worth of BSEG-FDTAG is archetypal and my logic is below:

BSEG-FDTAG = SY-DATUM + BSEG-ZBD1T. Assuming the values volition beryllium 08/31/2024

However, aft exiting the ZOBJECT, the worth of BSEG-FDTAG volition beryllium 00000000 again. Why does that happen?

The travel of FDTAG determination is similar this:

ZOBJECT> sapff001> ZOBJECT. 

The archetypal clip it volition spell done the ZOBJECT the FDTAG volition beryllium 08/31/2024. Then it volition spell to the program sapff001, there, the worth of FDTAG volition beryllium 00/00/0000 earlier computation.

There is simply a computation for FDTAD in sapff001 however, the conditions were not satisfied hence, I'm not getting the close results.