"Edit Script" opens UnityEngine.UI.dll instead of the script

If I select an object in the hierarchy, and then go to one of its scripts in the inspector, go to the gear and select "Edit Script", rather than opening the script, it opens a dll from unity itself: "C:\Program Files\Unity\Editor\Data\UnityExtensions\Unity\GUISystem\UnityEngine.UI.dll". I'm using notepad++, but whatever external editor I select, it finds the same file. If I use the default monodevelop, it just opens monodevelop in the top level project folder. In both cases, it works fine when I open the script from the asset selection bit along the bottom, but I have to sort through all the scripts in my project.

Anyone know a fix for this?