This bug is NOT a duplicate of MC-68080.
MC-68080 is someone's report of general lag.
this report is of uneven movement of the camera that is unrelated to frame rate. frame rate does not drop because of this bug.

before the creation of a bug report, I take the time to search for duplicates, as asked. please read my reports carefully before accusing me of duplicating other bug reports.

thanks.

On my computer, specifically a newly generated singleplayer world, I noticed I did not move at a uniform rate. steve seems to jerk forward, stop for a fraction of a second, and jerk forward again, constantly, while in flight and on the ground. It originally looked as if Minecraft was running at less that 10 frames per second. but my head turned just like it should, and revealed the actual frame rate was normal (80 fps). the debug screen also did.

the choppy movement was NOT just a general lag spike caused by movement, as the frame rate did not drop while I moved.

the effect was not obvious on multiplayer that day. on multiplayer, the terrain I was on had already been generated. in singleplayer where this problem occurred, the world was still being generated. The singleplayer world was of type default, and did not seem to have an abundance of mobs, falling gravel, etc. that might have been causing lag.