silpho

@violine1101 seems to be right. I was experiencing this bug when my clouds were off. Turning clouds to Fast or Fancy fixes the problem. Changing graphics from Fancy to Fast didn't seem to make a difference to me though.

(This test was carried out in 1.15.2)

Confirmed to still be a bug in 13w04a

I thought it might have been due to how far through the Portal I stood, but that didn't seem to matter either.

Confirmed again in 1.4.4 Pre-release - Single player.
Survival Mode - Changes direction very frequently. Particularly when facing the sides of the Portal rather than straight in.
Creative Mode - Changes direction far less often. Seems to happen more often if you turn as you enter the Portal blocks - Possibly determining your rotation as you touch the block rather than when you are teleported.

Early testing seems to confirm Aidan's thoughts, Creative vs Survival does seem to make a difference.

I've investigated this issue in the past. It appears to be caused when the indoor-rain sound effect stops playing. So going in to a house starts the indoor sound effect and then going down into a mine stops the sound from being heard, that's when the major stutter happens.

Since the game uses the same actual sound effect for both indoor and outdoor rain, looks like the problem might be in the pitch-adjustment code. (Making a quick mod to make all rain sound the same fixed the stutter, but at the cost having the same noise inside and out).

Hope that's at least slightly helpful.

You're welcome 🙂 Happy to see this minor niggle being fixed.

Just so everyone is on the same page here...
Sand block - Can be placed by a player. Falls under gravity. Is not flammable and not affected by lava.
Sand item - Drops when a sand block is mined. Can be picked up. Is flammable and destroyed by lava.
Sand entity - Used by the game to show sand falling when nothing is underneath. Visual only, should never appear to be on fire but, before the bug fix, sometimes can.

Blocks and items are unaffected by this change. This only stops the entity from looking like it is on fire while the sand "falls" from one space to another. It doesn't affect gameplay in any way.

It's not the items that I'm talking about though, it's the sand block as it falls downwards. Cobblestone and obsidian aren't affected by this problem.

Also experiencing this myself. First noticed in 1.3.2, continued in to 1.4.2, but possibly a little less frequently. Happening in single player. Not tested in multiplayer. (CPU load often hits 100%, might be related to some sort of internal "lag")