I played around with the Chrome console yesterday. I removed the readonly attribute on the and found that typing in the date the first time works in multiple formats (DD/MM/YYYY, DD-MM-YYYY) The initial time we type in, the date picker goes to that date while you type and then converts the date to the standard format DD MMM YYYY. After you leave the box and click back in it, the date picker no longer works.
I saw this ticket about datepicker binding, that was merged, but I don’t know enough about javascript to figure out if this would solve the problem.