Upon entering the game my character jerks around and is unable to move. I have to break the block under me in order to be 'released' but this can be awkward as the jerking can knock the pointer off the block (and even worse if I was to land on a stone block)

I cant remember when this started but I believe it was around 1.4.6 and has continued. Having just downloaded 13w01a and went to test it on single player, the issue is still there.

It doesn't happen on creative as far as I have seen and tested.

Video is too large to be uploaded but one can be provided on youtube if required.