Sketch on a picked flat face or reference plane opens the sketch on it at once. With nothing
picked it no longer enters sketch mode: the reference planes and axes come up, and the plane or
flat face clicked next opens the sketch and puts them away. Esc or Cancel leaves without one.
A picked plane is used up by the sketch on it and dropped by Esc or a click on nothing, the plane
prompt is no longer replaced by a stale tool hint, and clicking the face a sketch was just
cancelled on picks that face again rather than the whole body.