The bug
Explosions can damage blocks outside of world border. Seems unintended considering you cannot damage/modify outside of the border in other ways.
Examples
beds exploding in the nether
creeper
fireball
tnt
tnt minecarts
Steps to Reproduce
Set the center of the world border to your current position and to 15 blocks wide.
/worldborder center ~ ~ /worldborder set 15
Place some TNT directly next to the world border and ignite it.
When the TNT explodes, take note as to whether or not explosions can damage blocks and set fires outside of the world border.
Observed Behavior
Explosions can damage blocks and set fires outside of the world border.
Expected Behavior
Explosions would not be able to damage blocks and set fires outside of the world border.
I wish this would get more attention. Seems pretty significant to me.