Simple example:

http://jsfiddle.net/8UtFE/3/

Using $.event.trigger('write') or $.event.trigger('open') can result in calling document.open() or document.write() if the propagation is not stopped. I scanned the standard list of methods available on the document object and these are the only two that can be called with no arguments and result in adverse effects. The rest will at least throw an error, which is caught by the wrapping try/catch. But calling open() or write() will wipe the current document.

This affects 1.9.1, in latest Chrome, Firefox, IE9, and I would expect any other browser with open/write available on the document object. (all?) This issue is not present in earlier versions of jQuery.

Given that #6170 avoided the window object to avoid inadvertently calling global methods, this issue feels similar.