I don't know if this is intentional, but since the bugzilla upgrade I can no longer set the Assigned-To: field on new bugs, nor change it on my existing bugs. Often I know who wants the bug (e.g. experimental ebuilds) and would rather save the wranglers the hassle of reassigning it. Of course, if this is intentional I'll just shut up.
*** This bug has been marked as a duplicate of 115796 ***
AFAIK this is nowadays intentional and it shouldn't be a duplicate of a "mixed" bug, which suggests this feature is an unsolved bug report.