I'm using a 930, running 8.1 update 1 + Demin. And the half press of the shutter button seems to do nothing at all. In either the basic Camera app, or Lumia Camera.
Also, has anyone got a good Lumia Camera user guide, because MS don't
Guides... here's one from Windows Central, one on Framing grids, and another one with advice and opinions... and how about this one from Pocket Now (a bit old but still useful) and, the most comprehensive of them all, the one from Microsoft.
In my 930 if I half press the shutter button, both the Lumia Camera (5) and the Lumia camera classic, the app starts the focus and if I fully press the picture is taken.