Do you have a page as a reference selector? In that case you probably have a warning in your consistency checks, saying something like 'Property 'XPath constraint' on the data grid of the select page has no effect when the page is used for selecting. Instead, the selection constraints properties of the reference selector can be used to constrain the selectable objects.'.
Note that setting an xpath constraint on a page is NOT the same as security. Security is defined in a domain model, you can ALWAYS get around page settings if you know the client/server API.