It looks like you're using the Next War mod. If that's the case you should probably mention that in your post.
If you were so concerned you'd not pull such a stunt.
I guess the cleanest solution is that a blockade should only work against a city when the blockading unit is in the cultural border of that city.
But then the civ might have to declare war on a third-party to break the blockade.That screws the possibility of blockading multiple cities from different civilizations in close proximity to eachother with a single ship. You'd need to have one ship in each civ's cultural boundary.
How about disabling blockading within your own cultural boundaries?
But then the civ might have to declare war on a third-party to break the blockade.
Not that I'm implying anything but you do realise that since you have open borders he can still attack and kill your privateer?
Can the AI be programmed to use Privateers properly? It certainly seems to me that the behaviour described is how Privateers should function, only that the AI should have an effective counter.
I guess the cleanest solution is that a blockade should only work against a city when the blockading unit is in the cultural border of that city.
IMHO this isn't a bug. It worked like that in RL too!
What's not correct is that the AI can't (or doesn't? I don't know, I don't even have BtS yet) put some defensive navy on the blockaded tiles to "open the trade route".