iconselectmenu('open') can't navigate with cursor in popup

My cursor is in a input (type=text). When I press the tabulator-key I will open a specific select. I tried this:

$('.selector').iconselectmenu('open');

Its working fine and open the popup and input have lost focus, BUT I can't use cursor to navigate in the open popup of selectbox.

When I click on selectbox the popup is open and I can navigate with cursors.

Is this a bug or something missing in my code?

I have tried:

$('.selector').iconselectmenu('open').focus();

$('.selector').iconselectmenu('open').iconselectmenu('focus'); no such method 'focus' for iconselectmenu widget instance

$('.selector').iconselectmenu('open').selectmenu('focus'); cannot call methods on selectmenu prior to initialization; attempted to call method 'focus'

Select was successfully created with:

$('.selector').iconselectmenu().iconselectmenu('menuWidget').addClass('ui-menu-icons customicons');