Zechnophobe
Strategy Lich
I've tried searching the forums, but I haven't seen this reported (either as a bug or a feature). Short time after finishing Great Library my cities cultural production was turned to large negative value (screenshot attached). Then my cultural boundaries oscillated -- on my turn city's cultural border included only the city tile, then on AI's turn, borders expanded to their normal position (along with announcement that city has gained Legendary culture). After a while there was no expansion.
I'm playing 0.34 with patch h. I'm playing the game in Linux, under Crossover games (a wine variant) so this may have something to do with the problem.
Do you have a save of that? I'm really curious myself what could cause that.
Negative culture of such astronomical values... Is very interesting.