Thresh currently has a visual bug with his lantern. Here are instructions on reproducing it:

1. Start any game (Summoner's Rift is fine).
2. Take a level in Thresh's W.
3. Move into a place where there is plenty of room to run in a straight line.
4. Use Thresh's W. It is easiest to use this as far as possible BEHIND you.
5. Run in the opposite direction, and intentionally break the range on Thresh's W.
6. Keep running. You will see Thresh's lantern aura moving ahead of Thresh, faster than Thresh is moving.

I have attached a screenshot of this in action.

Attached Images

LoLThreshVisualBug.jpg (432.5 KB, 56 views)

I was able to replicate this bug with Deep Terror Thresh and the lantern aura would move erratically around the screen. However, when I tried to replicate this bug with Classic Thresh, I did not notice the aura.
Also, on both skins, I noticed that upon breaking the range, Thresh and nearby allies would receive the shield from the ability if they had not already.

I can confirm this bug. It happens quite frequently with the normal skin for me. On VERY rare occasions, upon breaking the leap range of the lantern, I will gain a shield as normal, but then whoever I manage to sweep the glitched light over will gain a shield, too.

I also spotted this bug with the Deep Terror Thresh skin.

This issue also occurs when an ally clicks on the lantern.

Here is a video of the issue on YouTube: http://youtu.be/fOJxGlfUTxI

I find this to be a moderately annoying bug, mostly for two reasons;
1) It is unclear if this lantern after-effect "marker" has any effect on the game
2) It is visually distracting, since with the Deep Terror Thresh skin, it is a color somewhat similar to that of a targeting circle for casting.

I hope this helps clarify this issue, and show that it occurs very regularly in normal gameplay.

It looks like a deliberate effect; I don't think that's a bug. I've encountered it myself before. Could be tied to his hidden passive; I dunno.

-Chaz

Yeh maybe this has something to do with his hidden passive. He can shield people from a far if he lands the aura thing over them. That would be rather cool actually.