Value Error : list-style-type none is not a list-style-type value : none

I have been using the same menu system using lists on my web site for a couple of years and it has always validated OK.  

Today I received the message “Value Error : list-style-type none is not a list-style-type value : none”

Reference to the w3c schools etc clearly shows that “none” is a valid reference.

I think this is a new bug in the CSS validator.