CTRL-Z doesn't stop propagation of event stack on some browsers

Feedback from Doug's contact at Northeastern:

"Lastly, one very minor bug report: it says I can use command-z to undo my last annotation, and while that appears to be true, it also doesn't seem to capture/stop the propagation of that event as it also fires an undo event at the browser level, too (which, at least in Safari, causes the most recently closed tab to respawn"