We have several sites running under CMS6 and CMS7.  One site is no longer warning editors that an image is in use when they try to delete it.  Usually, if a resource is in use a warning like the attached appears.  I have combed EPiServer.config and other configuration between sites that are behaving as expected and the one that isn't.

Is there a config setting that ensures that a warning is presented to the user prior to deleting a file if it is in use?  Or has the sites softlink table got into strife? 

Help appreciated.

Thanks.