In every version of Minecraft up until this snapshot, if you've been an in inventory or other applicable GUI, after you exit out back into 'normal' (for lack of a better word) gameplay (where you're walking/looking around etc), this has always reset the mouse to the centre of the window so that when you open up another inventory, your mouse is in the middle for you to start quickly navigating the inventory again. However as of this snapshot the mouse retains its 'old' position.
This is by no means anything major but, can be a bit off putting considering how the game has handled since it was made pretty much, and if you've been messing around in other menus such as options etc, and you're just hitting escape to back out and then proceed into a chest for example, having the mouse nowhere near where you would expect is rather counter-intuitive.
Personally I find that moving the mouse is extremely counter intuitive.