External Editor API
You can still download beta 3 if you need this feature to work. I plan to release beta 5 ASAP (which should mean in 1-2 days) with a fix for the problem.
Sorry about any inconvenience this may have caused you!
Update: I gave into pressure and re-uploaded beta 4 with a fix for the external editor problem. So if you can’t wait for beta 5, you can also re-download beta 4.