The value for the Response Root Key in the Customize HTTP actions screen is not being saved. Entering a value, clicking "Update Resource", then re-opening the Customize HTTP actions screen does not show the value (it is not there).
Thanks for the report. Looking into this, I'll let you know when I have more info!
Yup, reproduced – looking into this now, I'll post updates!
This was a bug indeed, but it's now fixed. Sorry for the inconvenience!