Combobox initial selection error

The combo box on initial focus opens overlay with only one result displaying. If user attempts to click result showing an error of 'Iron List <item> should be a valid item' logs in the console. If you begin typing, or insert a space and remove it to have the full overlay result list shown this problem doesn't seem to exist. 

Background: the array being assigned to 'items' (for the overlay list) is being populated from a Firebase query and does have all data when the situation above is performed. 
               Environment:                          Node version: 6.6.0
                         Polymer version: '^1.2.0'
                         Vaadin-combo-box version: '^1.1.4'
 
If useful, here is the implementation for the combobox:

<vaadin-combo-box label="{{fieldLabel}}"
                      items="{{items}}"
                      allow-custom-value="{{allowNew}}"
                      on-value-changed="selectedName"
                      id="comboBox"></vaadin-combo-box>

Any ideas would be appreciated. Thanks!

Can you check that is your {{items}} an array of strings ["ab", "cd"...] or an array of objects? If it is objects, you would need also to provide item-label-path and item-value-path attributes to the combo-box. If that doesn't solve the issue can you provide a plunker/jsbin example where it can be reproduced?