I want to call a bean after a date is selected in a p:calendar. In my setup I have a @Named @ViewScoped Bean, the class ObWithDate is
This is most likely a lifecycle issue. The setter for your field is called before your listener executes. You should not use the listener to set your value.
The el expression on your listener is evaluated at render response phase of the previous request thus it holds the cum value "one step behind".
You should update your custom object from the setter of the calendar's date value.