I'm sure there's a description of this bug somewhere, but I noticed the same thing. It seems to occur when the computer is under a bit of stress for me.
I made a parkour map that required the player to teleport multiple times mid jump, and sometimes (especially when hosting a LAN, but sometimes when on single player) it would glitch me back to the most recent teleport position, even after landing.
It seems to occur ~1s after the teleport it glitches back to. It hasn't occurred for me since I got a new laptop.
stat.useItem.minecraft.shield does not exist either.
Confirmed for 14w18b, launcher version 1.4.2.
Method:
Note: Usually, HideFlags uses values of 0-31 (2^5 values). Adding another line to hide would make it use 0-63 (2^6 values).
I used a simple command,
give @p leather_chestplate 1 0 {display:,HideFlags:31}
to test it (this would hide all lines available to hide). The line still displayed.
As I said, adding the other line would bring the values to 63, so I tried
give @p leather_chestplate 1 0 {display:,HideFlags:63}
and got the same result.
Confirmed as of 15w42a