Please rewrite the 'blur' event handler to solve this issue.
$.extend($.fn.datebox.defaults, {
inputEvents: $.extend({},$.fn.combo.defaults.inputEvents, {
blur: function (e) {
$.fn.combo.defaults.inputEvents.blur(e);
var d = $(e.data.target);
d.datebox('setValue',d.datebox('getValue'));
}
})
});