Snaketales has it right.
They were filming the 2 films back-to-back, but started runing out of money. Originally, nothing bad happens to Lois, so there is no need to reverse time. I guess they wanted a 'big' finish, so they 'borrowed' the ending from part II, and reworked that film later on.
Kinda like how they blew up the Death Star in climax to Star Wars, and again in Return of the Jedi.