In the attached save, the Persian civilization allows itself to be destroyed. A vote in the Apostolic Palace comes up to assign Persepolis (the only Persian city) to me. The following turn, the city is granted to me. Persia actually votes, but rather than defy the resolution (meaning they'll stay in the game), they just vote "no", meaning they allow themselves to be destroyed.
Steps to reproduce (though I'm sure other choices will still make it happen):
1. Press Enter to end turn
2. Do not agree to open borders
3. Build a Privateer
4. Click to assign the Persian city of Persepolis to yourself
5. Vote Yes
6. Fortify the Privateer stack
7. End turn
Sorry, can't figure out the attachment system. Here's the save game: http://files-upload.com/files/596893/JurassicLizard AD-1876.CivBeyondSwordSave
Steps to reproduce (though I'm sure other choices will still make it happen):
1. Press Enter to end turn
2. Do not agree to open borders
3. Build a Privateer
4. Click to assign the Persian city of Persepolis to yourself
5. Vote Yes
6. Fortify the Privateer stack
7. End turn
Sorry, can't figure out the attachment system. Here's the save game: http://files-upload.com/files/596893/JurassicLizard AD-1876.CivBeyondSwordSave