Reproduced this with a build compiled from 2015Jun08 source and got the same error on the crash log. Note that this does not happen in Movie crop mode. Switching from AF to MF solves the problem but of course there's no point in pressing the shutter half way because it doesn't trigger the auto focus. On second thought, isn't continuous AF always on when in Movie mode? What's the point in pressing the shutter to half way?
shutter half press is used for silent pics, it can also be mapped to magic zoom, and some other things. There is an option in canon menu to turn of continuous af.