Installed this today. Got pointed to this piece of software by Slashdot - so expect a downpour if they try this feature :)
It's funny how you can still add keys following this very non-intuitive procedure (separate bug?):
1. Try to add the field - get the error
2. Click cancel
3. In the key editing tab click "OK"
4. Re-open your entry and be amazed how your cancelled field is now present.