I've attached movie. There I click on dropDown button and you can see, that someTimes dropDown appear, and sometimes focus disappear (click happened) but dropDown doesn't appear.

For editable comboBox, when click is done in a point, someTimes dropDown appear, sometimes it doesn't.

I've found this issue, while using this method for dropDown appearing.

protected void clickDropDownButton() {
        testedControl.mouse().click(1, new Point(testedControl.getScreenBounds().width - 15, testedControl.getScreenBounds().height - 15));
    }