posted 06-29-99 04:31 PM ET
It's simple, really 
The item by item list shows current leader, the overall shows historic leader.
So you may be, at this turn:
researching tech faster
stronger militarily
have more pop
have more energy reserves
control most territory,
but you may not be ahead on those items that contribute to AC score (reproduced below from Concepts.txt:
#ADVCONCEPT4
Your Alpha Centauri Score is computed as follows:
1) 1 point for each citizen of each base.
2) If you have won a Diplomatic or Economic victory, score:
a) 1 point for each citizen of a Pact Brother's base.
b) 1/2 point for each citizen of any other faction's base.
3) 1 point for each citizen of a surrendered base.
4) 1 point for each unit of commerce your bases are receiving.
5) 1 point for each technology discovered.
6) 10 points for each Transcendent Thought advance.
7) 25 points for each Secret Project
8) A Victory bonus if you have won the game.
Obviously during the game, until victory bonuses kick in, the most important are population and Secret Projects.
So you could be far ahead of the others in the ranking charts, yet be behind in the overall game scors 
googlie
Putting a spin on it