@PreDestroy is sometimes called once directly after @PostConstruct, sometimes called twice when triggering GET again

Question

i am currently faced with strange problems with @PreDestroy methods in Mojarra 2.2.14: The behaviour seems to be some kind of undefined. sometimes it is called one time directly after @PostConstruct, sometimes it is called twice when triggering the GET again. same when leaving current page: sometimes clear() is called, but most times not. @PostConstruct on the the other hand works as expected.

the result ist, that all fields of ProductDetailBean are null, wenn calling page "productDetails.xhtml".

are there some known issues about that @PreDestroy? Would be very nice, if someown could give some helpful info about this. what would be suitable workarounds? this bean has a lot of fields and i have a strong interest to clear everything up when user leaves page.

Sadly i can not change to CDI-Beans for now...

@ManagedBean(name="productDetail")  //javax.faces.bean.ManagedBean
@ViewScoped                        //javax.faces.bean.ViewScoped
public class ProductDetailBean implements Serializable {

      private String field;

      @PostConstruct
      public void init(){
        System.out.println("init Behaviour is ok, callend only once!");
        this.field = "blah";
      }


      @PreDestroy
      public void clear(){
        System.out.println("called one or multiple times after init() ");
        this.field = null;
      }

   public void setField(String field) {
     this.field = field;
   }

   public String getField() {
       return this.field;
   }

}