Do Assignments work today?

Posted on behalf of Ben Funkhouser. Original posting date 2014-11-03.
Hello,

I'm just wondering if, by updating the assignments on a task, that will be enough to change the owner?
I am posting this data to the task, and it is not changing the owner.

{
"package_id": "{packageId},
"is_shared": "true",
"parent_id": "{parentId},
"assignments": [
{
"person_id": {personId}
}
]
}

For now do I need to update both the assignments array and the owner_id property?