NA XP-82 Twin Mustang Ongoing Rebuild

I do not remember seeing this project mentioned on here, its the rebuild of the prototype Twin Mustang By Tom Reilly that is ongoing in America. see http://www.xp-82twinmustangproject.com/ progress is certainly impressive on this project.
This particular aircraft has Packard Merlins V-1650-23/25 which rotate in opposite directions. From Wikipedia came this interesting fact ‘The aircraft refused to become airborne during its first flight attempt. After a month of work North American engineers finally discovered that rotating the propellers to meet in the center on their upward turn created sufficient drag to cancel out all lift from the center wing section, one quarter of the aircraft’s total wing surface area. The engines and propellers were then exchanged, with their rotation meeting on the downward turn, and the problem was fully solved’.
Later aircraft had Allisons V-1710,s that rotated in the same direction, so why didnt one wing then suffer lack of lift?

Richard