You do understand that is just a regular combo box to show the difference from the custom drop down textbox? Or did you miss the instructions
City1 - Press ALT+Down or left-click. Text part of ComboBox (with or without dropdown button) is showed to benefit from AutoCorrect feature.
City2 - Press Alt+Down. Only dropdown list of ComboBox is used.
City3 - Regular ComboBox (just for comparison).