The buttons are simply for getting the menu style in the combobox drop down. The design I'm working with has menuitem-styled items with a combobox-style selection box. For similar examples you can check out the Font dropdown in Word 2013 (note the opentype font icon next to the font name is not displayed in the combobox selection box - just the font name) and the Style ComboBox in the References>Citations & Bibliography group.
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