If you go into key config, there's key bind as well as press mode. So you can pick press, release or continuous modes for binds. If you want to hold set it to continuous.So after months of being oblivious i finally realised that holding shift no longer holds your breath when aiming, seems they moved it to 'alt' ages ago... however i've noticed that you can now seemingly hold your breath forever, once you press alt he starts holding his breath and doesn't breath out until you press alt again... doesn't matter how long you wait between pressing it, the aim remains steady.
Odd