It is still happening till now.

 

When you are loading up the world, and if you are extremely unlucky to encounter this bug, the log tells you that you have entered a single-player world, but the GUI brings you back to the title screen.

Then when you tries to reload by re-entering the target world, the game unloads the world and loads it back! Usually you may be sent back to the original spawn-point...

I know this behavior too. I think this should be on bug report.

(Or is this intended feature? I want to know)

 

Anyway, the mechanism would be in calling Minecraft#displayGuiScreen(null);

  while world is not loaded so Minecraft#theWorld is null.

It isnt any bug.

The logs still output normally, for example:

 

Loading world: How-many%

Player has joined the world

 

and then it brings me back.

It isnt any bug.

The logs still output normally, for example:

 

Loading world: How-many%

Player has joined the world

 

and then it brings me back.

So is it problem with your mod? Then you should describe what your mod does.

I'll just note that I too had this issue (on 1.. In my dev - randomly (but seriously - it was like few times, 0.1% to happen).

I don't know why but I always felt like it was internet fault. Whenever that happened (very rare) - I was downloading something and had huge lag, almost couldnt login into game (mojang auth was taking about 10sec).

 

So just saying - it might be forge/mc fault.