When I'm in the middle of walking or sprinting performing a left or right click seems to stop me from moving, even with the movement keys still held down. I have to re-hit the movement keys to continue walking or sprinting again, and make sure not to click with the mouse again... Very annoying, I ended up downgrading back to 1.4.2 to overcome these issues.

Also, shift-clicking seems to be broken. I can't shift-click items while a chest or furnace menu is open, nothing happens. Also works fie in 1.4.2.

I found out the issue doesn't happen while playing in full screen, only in windowed mode.