Last modified: 2014-09-05 14:31:59 UTC
Possibly related to bug 57396. When a User account is renamed, the new username appears next to the user's posts (expected behavior), but replying to the renamed user populates the old username into the reply form (unexpected and confusing).
That code had changed since this bug report, and this was likely no longer happening. We've recently removed the prefilled username anyway, so this definitely can't happen anymore.