Step to reproduice
In ibexa v4.5.2  :

•  Edite the article or existing content type and add a new ezselection field 
•  Keep the checkbox "multiple choice" ** NOT** checked.
• Add two options
• Create a new content of this content type
• Check the selection behavior, the default checked is All

Expected result:
 The default label in the selection field is "All" but should be "None" since this is not a multiple choice selection.