Bug 1037655 - Move popup icon live preview into a preview icon in the editor 

I could be wrong here, but seeing this makes me think that it will have the incorrect icon any time the editor is opened from an existing popup event where the default icon isn't selected.

I could be wrong though and you're taking advantage of an order of events that have not occurred yet (IE, we haven't set the value in the select element for the icon and it happens after the listener you add below, causing it to be handled there).

Something to keep an eye on.