Update on my above comment...
I went to the video settings and unchecked the anti-aliasing just to try something different...the movement issues worsened. So i reset the anti-aliasing and looked at the chunks rendering bar next. It was set at 64, so I reduced it and noticed that my gameplay was fixed! I went to set it back to 64 just to see if the problem returned and found that I couldn't...the new maximum is now 44, and I couldn't put it back to 64 even if I wanted to. However, when I went in to check gameplay after setting it to the new maximum of 44, I noticed that I still no longer had any movement issues. Hope this helps others with the keyboard movement problems.
I have the same issue you have described and tried the same steps to resolve it with no success. I play on a laptop and use a keyboard/mouse combination. I have the same issue with old saves as well as with newly created worlds since the update. It is like there is a lag between keyboard command and game recognition of that command at times. Once, I tried 'shimmying' the mouse and making various keystroke direction changes while stuck in that forward movement only to have those same moves acted out after a brief delay (after I had already removed my hands from the keyboard). When I went to a friend's realm, I did not have the movement problem...it seems to be only on my generated worlds, which is odd. So I have been able to enjoy the nether update while playing on friends realms but not on any my worlds, old or new.
Sorry it didn't work for you!
I went back into my game today and once again had the same movement/lag problem. I redid the steps I mentioned:
1) Reduced chunks to 24,
2) Reduced Anti-aliasing to 1
3) Clicked 'off' the texel anti-aliasing
Then resumed my game, saw everything working well again, and went back into settings and reset my settings to what they were when first opened the game:
1) Returned chunks to 44
2) Returned Anti-aliasing to 8
3) Clicked the texel anti-aliasing back 'On'
Once again, resuming my game let me play without the keyboard lag. Shame this didn't work for you, but hopefully it gives a clue as to what may fix the problem for all affected by it! In the meantime, I guess I will have to do this each time before extended gameplay.