Undo Shortcut in Unit Planner

I love the UI of the Unit Planner. Very-well designed :) Unfortunately, I am finding it to be very glitchy and things are jumping around where I don't want them while dragging units and lessons on the timeline. At the very least it would be help to have the Ctrl + Z shortcut for 'Undo' so that I could try dragging the unit into the correct spot again.