Closing dialogs triggers beforeunload in IE

When using Internet Explorer, closing a dialog such as the image or link dialog triggers the beforeunload event. This does not happen in chrome or other browsers.

This event is bound to the window object, so there is no way to differentiate it from the closing of the window. I suspect this is due to removing an iframe from the DOM? But can not be sure.

In any case, this is quite annoying, there are many plugins out there outside of ckeditor that tie in to the beforeunload event, and excess triggering of this event only in IE is becoming more and more annoying.