Static vs. Dynamic button

When creating a static button through the AB I select the DROP-TARGET as true AND the DROP-FILE-NOTIFY trigger just works.

But when creating a dynamic button like this

DEFINE VARIABLE hanButton AS HANDLE      NO-UNDO.

  CREATE BUTTON hanButton
    ASSIGN
      FRAME = FRAME {&FRAME-NAME}:HANDLE
      VISIBLE = TRUE
      SENSITIVE = TRUE
      HIDDEN = FALSE
      SELECTABLE = TRUE
      DROP-TARGET = TRUE

    TRIGGERS:

      ON DROP-FILE-NOTIFY RUN DropFile(hanButton).      
    END TRIGGERS.

it seems that DROP-FILE-NOTIFY doesn't work.

Is this normal behaviour. Where is this proper documented?

But most important what am I doing wrong