Steal technology - bug or rule?

[ruoyu]

I am runing an Emperor game level with 16 civ at huge map. I found I can never catch up the technology so I set science to 0 to get more money to buy latest technology. Techs in ancient era are quite cheap that I still can buy from one civ and sell to another one to make profit. However, when I enter the newer era I found techs are so expensive and even I can't sell it at high price. So I decide to bet on my luck to steal from enemy which is a llittle bit cheaper.

The first few stealing was fine and I get one tech at each time. Then when I try to steal a tech from one civ who has three techs ahead of mine. After I stole the first one, the computer asked me if I want see the big picture. Usually I skip it and continue on but this time I choose show me the big picture and then I found I can steal again for freeeeee.....!!! Ha! A great deal, finally I got another 2 techs for free!!!

The question is: can someone tell me if it's a bug or the game rule?

[DesertWolf]

could it be that you just entered a new age of time while playing with a techology civ?

then you'll get a new tch each time you enter a new timeage

[ruoyu]

no, I am in middle of the industrial age and my civ is not a scientific civ.