The old bugzilla did this.
The old didnt really do it. It displayed what the owner would be if you didnt change component in the bug report. The proper behviour for the new Bugzilla would be to leave it as is because it is basically saying that if you change the component associated with the bug report, it will assign the owner to be the default owner of the new component if different than the current owner of the bug report.
*** Bug 75993 has been marked as a duplicate of this bug. ***