Where are all the unit/integration tests for the APIs that this damned button is calling? Hindsight being 20/20, but I cannot imagine not asserting that a newly created/re-enabled root user has a non-empty password.
I suppose you could write an assertion that the code didn't enable the root user, but I'm pretty sure that no password-validation routine anywhere in the history of the world has ever had a test case to make sure it didn't modify the account while validating it.
These are unknown unknowns. If you knew enough to write the right test, you wouldn't have written the bug in the first place.