Losing to an AI's Cultural Victory

I had lately a situation, that hasn't happened to me for over a year now. I've lost a game (Immortal) to an AI that has gotten a Cultural Victory. I can only remember like 2 or 3 games where I've lost in such a way and it was way ago in Vanilla, where Constitution was giving 100% culture boost to cities with wonders build in.

So the question is: has something like that happened to you, what were the circumstances etc.

I can give additional details. It was a 4 player archipelago map. The specific is, that it was quick pace - I usually play on standard and this might be a difference in this case.

I could have won the game on reloading a 20 - 30 turns, cause I was going for science victory, but lingered with the techs (as I went for militaristic techs first). I was covered on diplo, tech and military wins, therefore I lingered, did not check the cultural status though as I did not susspect the AI being able to go for it.

I've had something like that happen to me a few weeks back.

Was playing on an Amazon map with the Maya (I wanted to try out their odd UA) and I was able to pick up the +1 culture to jungle tiles belief early so I was something of a cultural powerhouse most of the game. As time went on though I got bogged down with wars against Spain and the Iroquois and the jungle terrain and lack of hills or screwing with my ability to get stuff built at the same pace I was used to. I also was the religious super-power for most of the game with able 50% of all cities on the map following my religion. Little did I know, probably because I was too lazy to check, that Arabia on the other side of the map was going a culture route and was able to knock me out in the 1800's or something. I had artillery and early planes rolling right over the Iroquois and by the time I got near Ariabia.....

Poof!

I had no idea that they were that far along. My 1 or 2 spies were parked in my capital and in the capitals of the Civ's I was actually at war with. If I had known I would have marched my entire army at them asap.