It took me a long time to realize this, so I will share.
When you quick-save a magic sheet, pressing [undo] is supposed to revert back to the quick-save. Control&X is the shortcut key for undo but it doesn't work when the magic sheet is open for editing. Control-X cuts any selected MS object but does nothing when no object is selected.
There should be an "undo" icon next to the "quick save" icon. Ideally undo would work without the need for quick save, and it would undo a different edit each time it is pressed.
Workarounds for us Nomad users:
Map "undo" to a macro
Map "undo" to a second MS and run it from there
Close the editor and then use Control-X to undo. You may need to undo multiple commands if you do this.