What is the AI behind Gan Ning's targets? It seems like he keeps on following me where ever I go. When I'm using Sun Ce, he kept on patrolling the Yangtze, making it difficult to launch naval invasion of Liu Bei. When I'm using Liu Bei, he kept on blockading XiaPi and my other coastal cities. Is it just my imagination, or does he have it out for the human players?

It probably has to do with the Barbarian State's targeting system. Basically they pick a target and rarely change it. That also explains the behavior of the AI on barbarian heavy maps where they seem to bypass civs on a whim and only target one. The human player has a high priority for this targeting I guess, but it certainly happens to the AI too.

When Gan Ning has his famous sea-lord promotion, he will form a naval legion and use the privateer AI.