Thats why its not a focus hunting behaviour. Its more subtle kind of slow focus across 3 seconds. You can do an experiment, by leaving the camera on the table, you will observe that the liveview will slowly gain focus onto the mid point. The speed is totally different from the focusing we get when we press the shutter release button. I dont think this poses issues other than using up more battery.
I just noticed this focus hunting behavior in both the kit len and sigma lens. I guessed it did not really bother me too much.
But i do hope they put a option to disable away the function to see the differences. Maybe increase in battery life or even faster focus?