Mine was when I scouted at the point of the city teleporting. I Launched scouts on a Thuringia City, got a scout report on a city in Saxony. I mailed the new owner and found out she had just conquered and teleported the city. My Scouts had a long long walk home.

New City owner was pretty mad I knew where she had moved the city too!

I still wonder if it was a bug or if it could be done again?