If Bell Borca is in play with power 0 (used to simplify the explanation), and a card with aftermath is cast from the graveyard then Bell Borca's total power will be set to the mana value of the bottom half of the aftermath card instead of the total mana value.

For a discrete example
i) Bell Borca is in play with power 0
ii) Injury is cast from the graveyard
iii)Injury Resolves
iv) Bell Borca Notes the mana value of Insult//injury as being 3 and has its power set to 3

I am resubmitting this bug report as It is still happening and I have confirmed multiple times with MTG Judge Chat that this is not how it is meant to work.