Set a format "a h:m:s" to the timebox cannot work correctly

For example,

1. Please delete the "AM/PM" and then type 121212, it should appear "AM/PM" 12:12:12
2. Please delete the whole number area, for example 12:12:12, and then type 121212, it should appear "AM/PM" 12:12:12
<timebox format="a h:m:s" width="150px" onCreate="self.value = new Date()" />