If I understand the security doc correctly I shouldn't get 401 responses when I have mixed="hide" in the layers.properties file. But I've across two cases when I do get 401 responses, here they are:
user sends a WMS GetCapabilities request, user provides incorrect username/password in the request
user sends a WMS GetCapabilities request, user provides correct username/password in the request, but user doesn't have write permissions for all the layers
I've encountered this problem in 1.7.6. Does the problem also exist in the 2.x series?