When deciding whether or not to display a status change for a task, the TaskWatcher code only considers state. So, if a task is reassigned without changing state (e.g. a manual reassignment when the task is already assigned to a different host), the task watching output does not show the detail.
This doesn't come up too often and doesn't really cause a problem, but it would be nice to fix at some point.
This issue has been migrated to Fedora Forge: https://forge.fedoraproject.org/koji/koji/issues/4509
Please continue any further discussion there.