I’d half call this a bug but really I suppose it’s a missing enhancement.
When you delete an enivronment variable in the CircleCI project settings there is NO double check that you actually want to delete that key. Now the reason this to me is an issue is two fold - one the removal happens so damn quick you sometimes don’t think it took and you may click again before reading the env var name back all the way to the left - some may call this lazy but when you’re pressed for time things happen.
A more concrete reason though is simply an accident. I’m sure everyone reading this has clicked a button by accident. If someone accidentally clicks delete on an env var that is it. There is no going back. Please for the sake of sanity add a confirmation button before you just delete an env var.