-start with a new project or use an old one, doesn´t matter
-create a midi track or use an already present one
-create a midi event or use an already present one
-select it and open score editor in page view
-drag one bar line siedways
-hit ctrl+Z to undo it
-> nothing happens - but in the undo list this step is greyed out
-close the score editor and reopen it
-> the bar line dragging now is undone!
conclusion: to actually see the undo of dragging a bar line you have to reopen the score editor.
Cubase Pro 8.05, Windows 7 SP1