Just noticed a bug where upon reloading a saved game, buildings that are currently being upgraded are not considered when calculating your borders, and you will temporarily lose any border extensions that you previously had if you save and re-load before the upgrade is finished.  In my capital city, I built a library that had extended my border over a life shard.  That library is the furthest building on the southeast side, therefore my borders are dependent on that library being there.

Many turns later, I started upgrading that library.  Before the upgrade finished, I saved the game (manually, not autosave) and quit.  Upon re-loading the game, this library is no longer being used to calculate my borders.  I know this because my borders were no longer covering the life shard and the life shrine was destroyed next turn.  Once the library upgrade finished, my border extended again and I was able to re-build the life shard.