Minecraft wiki entry for Development_versions, associated text: The floating-point precision used for the location of where certain particles and entities appear was increased to 64-bit (double-precision), from 32-bit (single-precision).
This fixes many issues regarding certain types of particles and entities not appearing at the right places when far away from the center of the world, especially beyond 16,777,216 (224) blocks. The following list includes instances that are known and confirmed to be fixed:
Particles
Fishing particles[27]
Squid ink particles[28]
End gateway particles[29]
Conduit particles[30]
Impact particles when entity has fallen from height on to block[31]
Sweeping attack particles[31]
Damage heart particles[31]
Particles appearing when using the /particle command[31]
Mycelium particles[31]
Underwater particles[31]
Nether portal particles[31]
End portal particles[31]
Brewing stand particles[31]
Spawner particles[31]
Barrier particles[31]
Armor stand breaking particles[31]
Suspended gravity affected block particles[31]
Entities
Primed TNT entities.[32] However, indirectly ignited TNT from other explosions is still affected.[33]
Block entities
The floating book above placed enchanting tables is now correctly rotated towards the direction of where a nearby player is at high coordinates.[34] However, there are still issues with the book not opening early enough.[35]