Spectator location 1tick delayed bug

In Minecraft Java Edition, when a spectator is spectating another player or entity, the spectator's position on the server side is updated 1 tick later than the target's movement.

This delay occurs regardless of whether the target is moving by player input or via commands such as /tp.

This issue did not exist in versions prior to 1.21.2, but can be consistently reproduced in 1.21.2 and all newer versions.

Steps to Reproduce:

1. /scoreboard objectives add x dummy

2. Create a repeating command block, set it to “Always Active” and set the command to

   execute at @a as @e[distance=..1] store result score @s x run data get entity @s Pos[0]

3. /scoreboard objectives setdisplay sidebar x

4. Place an armor stand

5. Switch to spectator mode (F3+N)

6. Spectate the armor stand (You should then be seeing both your own and the armor stand’s x coodinate on screen

7. /tick rate 1

8. /execute as @n[type=minecraft:armor_stand] at @s run teleport ~1 ~ ~