video: http://puu.sh/bFRaw.mp4
record at 30 fps but I was playing it 100 fps

Well what i am using is:
flans mod from the latest avalible files here on github
forge build 1180 for 1.7.10
and my content packs but it is hapening with flans armor aswell

I made a build and used it on a normal minecraft setup, not on the dev setup or anything, playing it as ussual

Before the old one was closed flan asked is that hapenned using diamond armor, well it does
http://puu.sh/bFSb2.png

and its not performace issues like godgodgodgodgo said as I am on 100 fps with the armor desync

I have this on vanilla minecraft, therefor, it's a minecraft bug.