Hm, okay, its weird. it works sometimes. From what I can work out:
Enable OneView. Move to say a view where it says “front” in the top right. Then click on linear dimension. Nothing happens and its not letting you create a linear dimension in Z. But, if you then right-click it will repeat the dimension command and now the cplane will automatically switch to a front view one and you can draw a dimension in Z.
But why only when I right-click and not when I just click on the button for linear dimension?