The last message wasn't quite what you wanted.  You are using Movement Mouse Mode which has its own special Undo Move button, while the code I gave you undoes the last normal move (not using the move selection mode).  So here is the shortcuts file undomove.py with the space key defined to run the Movement Mouse Mode undo move button.  It also has the z key running the general undo move (menu Tools / Movement / Undo Move).

Tom