I have a possibly similar problem. I was exploring the Nether and found a missing chunk (a vertical column with nothing in it). Shortly afterwards the game slowed down to unusability. I quit out, restarted the computer, and restarted Minecraft: it was generally impossible to start that particular world at all, as it would either freeze up or return to the start screen. I updated my video drivers; no improvement. Occasionally I would get into the game but about half the landscape was missing and response time was extremely long.
I enabled the latest snapshot 14w30c. This allowed the game to start but response time is still extremely low.
I attach a screenshot of the missing chunk and a forced-crash crash report.
This still happens in 1.7.9. I have also seen it happen with a cow that spawned very high up on a block jutting out of a vertical cliff. The cow would appear to fall to the ground at the base of the cliff and then displace back up to its starting point. But it seems to happen much more often with spiders.
I have just seen this in 1.7.2. I had explored an area previously in 1.6.4 and in 1.7.2, but then went far away. When I came back, one chunk had dramatically changed--it was about 15 blocks higher than before, with perfectly straight sheer sides. I found an old map of the area and examined it, and could actually watch the old terrain (snowy tundra) being replaced by the new terrain (extreme hills, I think). I suspect this is an instance of this bug, made particularly spectacular because it put 1.7.2 terrain in an older section of my world.
This bug still exists in 1.7.2 and it occurs in at least three circumstances: getting off a horse, getting out of a minecart, getting out of bed. I have a bed that reliably throws me through a glass wall, and tonight I had a horse throw me through a stone wall.
This is still happening in 1.6.4. Also now that my cats have gotten up due to an attack on me, they will not sit down again. So all my dogs are permanently sitting, and all my cats are permanently not-sitting. I'm not sure which is the more annoying!
Sitting cats teleport to me in 1.6.2 single-player survival. It does not seem to involve my being hit by a mob. I have seen both short (10-20 blocks) and very long (500+ blocks) teleports. The cats are sitting when they arrive but can be stood up normally. It happens every few days. If I have multiple cats, usually only one teleports at a time.
I just had this happen in 1.8-pre3. I had five item frames on the wall with maps, and wanted to move them elsewhere. When I hit them, I only obtained three frames and three maps; two had vanished. I searched all adjacent areas with no success.