Manage Orders Sort settings

The manage orders page "Ship By Date" sorting options no longer sort by ship by date. I just noticed today that my orders are not correctly sorting by their ship by date. I have orders that need to ship by today listed underneath orders that don't have to ship untill tomorrow. They're all mixed in. This happens sorting by Ascending and Descending.

I did find that you can sort by Status and get the correct sort order. I'm simply confused as to why Ship By date doesn't sort by the ship by date.