This is something we recently started doing. If email sent to your email address bounces with an error message like, "This email address doesn't exist", then your email may eventually be changed to u...@bounces.invalid. (It's not possible for users to change their email address to something ending in .invalid, so this can only be an administrative change.) Because your old email didn't exist, somebody could've registered your non-existent email address and used that to steal your account.
I didn't particularly intend for the trust warning to appear for these automatic changes, but it's a niche situation and a bit difficult to fix, so I probably won't fix this unless several other people complain. It only lasts 30 days, after all.
Thank you very much @theymos for the reply. I just remember that I use an e-mail that I plan to create uniquely for my bitcointalk but I forget to do so like many years ago.
I will keep the thread open for a while for anyone who has anything to say on this update. I already updated the OP to include @theymos official response and mark the title as solve to help other user informed in case they encounter same confusion like what I did. Thanks guys!