Descriptive Problem Summary:
The example mob i'm going to work off of is our ghost/observer in ss13. this is it's effective animate_movement and sight:
animate_movement = 2
sight = 60

(client.mob == client.eye) //true
(pixel_movement) //false

When I join a game and hit observe to spectate the round, the game will spawn this mob at the late join spawn point (an 'arrivals shuttle') then set it's key to my key to connect my client to the mob.

The issue is that when it does this, the client's center will jump to the tile between my client's current eye, but just before the new eye location, then glide to the new eye

This actually happens with client.mob, not client.eye, but also happens if you just change the eye, and not the mob.

Meat of the issue:

If my client's current mob/eye was at 1,1,1 and i moved the client's mob/eye to a new mob/obj located at 10,1,1 it's jumping to 9,1,1 then gliding to 10,1,1.

Other Notes

It will do this as well for loc changes of the client's mob or eye.

It will do this with any of our mobs, or when we use the verb to set our eye to an object to follow it around.

It will do this when a 511 client connects to a 510 server, as well as a 511.1349 server.

Testing

You may join /tg/station at byond://game.tgstation13.org:1337 or our 511 test server at byond://game.tgstation13.org:9337 with a 511 client and click observe to test this effect. after that, you can double click on any tile more then 2 tiles away to jump to it to also observe the effect.