ferretbacon
Obsessor
This is the second time I've encountered this, so it wasn't a one-off. If you build an Entertainment District in City A with an Arena, then move to City B and try to build the Colosseum adjacent to that ED, you won't be able to. The Colosseum is available to build in City A as normal.
No, this has nothing to do with which city is working the tile.
No, this has nothing to do with which city is working the tile.