Dynamic Combobox Dropdown

I cannot view the dropdown list when clicking on the down arrow image. I am loading the list dynamic xml. The list only appears when I type a character in the field. Is is possible to view the dropdown list with just clicking the arrow?

In case of dynamical loading ( when data fetched from server as list of suggestions ) there is no way to show list of options for “empty” fileld, because there is no suggestion for it.
It possible to enable asking suggestions for empty field as well, but in result each combobox will send request to server side even if it is empty

just comment next line in source code
dhtmlxcombo.js line 852
if (text=="") { this.closeAll();  return this.clearAll();   }