None of your changes will have been lost; if there are changes, backspace will trigger an "are you sure?" question. All you'll have lost is cursor position and the what you wrote into the auto-cite box (which is probably still in your paste buffer), right?
No, it doesn't. I agree that it should trigger an "Are you sure?" dialog box, but it doesn't.
The reason I hit the backspace key is because the auto-cite box was filled with useless information. I had the URL in my paste buffer. I did not, unfortunately, have the entire rest of the unsaved changes to the article in my paste buffer. I lost a non-trivial amount of work.
I cannot reproduce in firefox 42 ubuntu, at my enwiki user sandbox, no matter what i try. I tried a few variations, as well as the exact sequence described, and either the browser-warning or VE discard edit warning will always appear, or just the character/element before the cursor is deleted. :-/
Can you explain why your browser didn't show "Are you sure?"? Does it fail to do this in other contexts? That's a UBN; this is a WONTFIX.
Same here. In Firefox 70.0b5 on macOS 10.14.6, I can reproduce that backspace over a generated-but-not-inserted citation triggers the discard-edit warning (which is undesirable behavior but not high-priority problem), but I can't reproduce anything that bypasses the warning.
I'll amend the title and description to reflect that.