Here is my case: the bone some how choose the longer route to rotate instead of the shorter route as usually
It happen when I try to rotate bone with short route like the (first case) then it automatically turn into long route (the second case). You can see the difference between short route and long route in the Graph here:

This video showing I try to make short route and it suddenly turn into long route:
https://vimeo.com/571663921
And this is how it rotate in the longer route:

Also I really love the new Graph editor, it make the 3. version feel like stone age compared to 4. version.
I hope this rotate problem is not cause by Graph editor
I just delete the rotate frame and redo the frame and the problem go away. But this bug occur quite frenquently for me after update to version 4.

Nate написав

How did you create the rotate key? Was it using the rotate tool, pose tool, or typing a value? Can you give step-by-step instructions so we can make it happen ourselves?

You can check you my video here, I using only the mouse alone, no typing at all.
https://vimeo.com/571663921
The bone is just a child bone and didn't have any IK or contraint attract to it. I hide all other bone in the video so you can see it more easily

Nate написав

Thanks, though I'm not able to get it to happen. It may only happen with specific bone rotations. Can you post or email the project file? contact@esotericsoftware.com

Thank, Here is the project itself:
The Bone Bug is the one you need to rotate by using mouse. This video is how I reproduct the bug, the bug not alway occur all the time. It only occur 2 times in this video.
https://vimeo.com/manage/videos/572144360

Nate написав

Thanks! We've fixed this problem in 4.0.03. Cheers! :beer:

Damn, that was fast. Thank you guy 8)