Seems like you've got some apples and oranges going here... There's a difference between setting the values into a bean, and getting values from the bean to populate an HTML form control. This statement:
uses the value of the amount property already set into the currentshipment bean to set the VALUE attribute of the input field. No bean setting is performed; just retrieval. This statement:
has no bean interaction whatsoever when the page is being constructed. Like any other form field, it will submit its value when the form is submitted which could be used to populate a bean field on the submission request. This statement:
will match any submission parameter to bean properties and set them.