Undo brush to original state [AP]

[shojtsy]

When using the undo brush in AP 1.6 by default it paints the original state of the image. I can modify this by clicking on the camera icon in the history panel next to one of the earlier states. After painting with one state selected in history panel, I would like to again paint to the original state, as if no camera icon would be selected. But there doesn't seem to be a way to clear the camera icon from history panel. I can only move it to other states, but then there is no way to undo-brush to the original state.