System Information
Win7 x64, GTX 560

Blender Version
Broken: git latest (6c329304)
Worked: unknown

Short description of error
The WM notification listener image_listener does this:

Object *ob = (Object *)wmn->reference;
if (ob && (ob->mode & OB_MODE_EDIT))

If this is happening after a Python script has run, it's entirely possible that wmn->reference is a hanging pointer.

Other listener functions check whether reference == NULL without actually trying to dereference it.

Exact steps for others to reproduce the error
Unfortunately I don't have a simple repro for this. I can trigger the crash reliably by running a very complex script on a very complex file; the crash happens when the Image Editor tries to refresh after the script finishes.