This question already has an answer here:
Observe the following (bad) question on Japanese.SE: What does "jukai" mean?
The question reports the following in the close banner:
Now, I happen to know that "user458" (the same user who made the last edit to the question on Nov 1 '11 at 23:35) was known as "sawa" before having their account removed. Shouldn't references to the user in the close banner also be anonymized to "user458"? Obviously, we're never going to succeed at perfectly anonymizing the user because of stuff like @mentions in the comments, but it seems like "system text" like the close banners at least ought to anonymize correctly.
(I suspect that protection and deletion banners may have the same issue, though I haven't encountered any posts that were protected or deleted by a now-deleted user yet.)
(Is this a duplicate of Further anonymize deleted accounts by changing the username in close/delete notices? animuson marked it status-completed, so I'm not sure what's up.)