My general fix for this is to add autocomplete: discourse but I don’t think this is correct in this case.
This is actually not exactly the same as this broken chrome behavior: https://bugs.chromium.org/p/chromium/issues/detail?id=587466
Somehow, some extension is adding text to new-account-challenge after we explicitly set it from here: discourse/app/assets/javascripts/discourse/controllers/create-account.js.es6 at 6de254f64263d7e3cc223404348c03e23c85d904 · discourse/discourse · GitHub
This is clearly bad browser extension behavior to me. Why is it touching an INPUT after it already has text in it?
I am not sure there is anything we can do here short of isolate what browser extension is causing this and raising an issue with the authors of said extension.