EDIT: It's been quite a while since the original report, and I'd like to update it with a lot more information.
It seems that when using the /tp command, the server and the client often have major disagreements about the rotation, momentum, and position of the player. When I filed the original report, it seemed to only result in the character's rotation being set to 0,0 and some occasionally choppy movement.
Now though, teleports seem to always result in choppy movement. Information about the teleport seems to be outdated, so to speak. It's most evident in the second attachment. When you have a series of teleports, any movement during the process is almost completely unpreserved. Sometimes even prior teleports are disregarded by the client leading to the character seemingly falling through the floor. The server always seems to get it right and the client eventually agrees, but until then, the process is an eyesore.
Viewing the two attachments, the first from 14w03b, the second from 1.8-pre1, you can see the major degradation of this feature over the seven months.
Linked issues
is duplicated by 2
Attachments
Comments 10

Is this still a concern in the current Minecraft version 14w11b or later? If so, please update the affected versions in order to best aid Mojang ensuring bugs are still valid in the latest releases/pre-releases. - bot
This is still an occasional issue. I'm recording a video in a minute showing the issue, and I'll upload either it or a GIF. I'm not sure if they're related, but it appears that momentum and direction are occasionally unpreserved during relative teleporting.
While I cannot upload any video due to connection restraints, I can state that this is still a minor issue in the latest versions. It's odd now though, as it seems that rotation and momentum sometimes graphically glitch, showing you in a different position than you should be, but only for a frame or two before being corrected. It's as if the sever/client (I'm running locally, for the record.) are out of sync, ever so slightly.
Upon further testing this is still a major issue in my newest build. Essentially, I'm using a series of /clone and /tp commands to simulate an elevator. Each of /tp and /clone commands are each delayed by two ticks by a Repeater on the second setting, powering each simultaneously. While the /clone commands seem to work rather fantastically, the /tp commands are incredibly buggy.
In transit, my view and position will randomly revert to whatever my position was at the start of the elevator, ignoring the y-axis, frequently jumping back again and allowing me to move around. Occasionally, I am reverted to the start of the elevator, taking into account the y-axis. Furthermore, the /tp commands end up being a tad behind the /clone commands in some cases, despite being powered simultaneously, leading occasionally to a rather jumpy ride. In fact, the animated GIF attached to the report is incredibly mild, as it seems to have gotten much worse since the initial report.
Our home Internet service is set up now and I'm only a few hours short of having the project ready for demonstration. If necessary, I'll soon be able to record video of this issue, as well as provide a download for the project. I was hoping that I could demonstrate this before the snapshot cycle was over.
Here is a particularly glaring example of the issue, exemplifying all of the issues that I am having.
https://bugs.mojang.com/secure/attachment/79857/UnconsciousWellgroomedHypsilophodon%5B1%5D.gif
can confirm in 1.8.6
when I keep teleporting myself up with a setblock clock, I cannot change where I look, or move to, it just resets me at the first rotation/momentum

Can't confirm in 1.9
Moving is smooth, don't fall through blocks (with clone), can look anywhere I want
anybody else still able to reproduce?
It's been over a year since the question was asked, please respond to the question or attach the files requests and keep the ticket updated.
[^UnconsciousWellgroomedHypsilophodon[1].gif]