bug found?

Hi folks,

following pages refer a keyword called inset for box-shadow:
http://www.css3files.com/shadow/
https://developer.mozilla.org/En/CSS/-moz-box-shadow
so the spec does:
http://www.w3.org/TR/css3-background/#the-box-shadow

While developing my new webpage i receive errors relating to this keyword:
http://jigsaw.w3.org/css-validator/validator?uri=http%3A%2F%2Fwww.exklusive-standards.de&profile=css3
(the last 3, please ignore the first 6 errors)

saying "is an incorrect operator".

If i delete the word "inset" those errors disappear, also this message is a little confusing, 'cos the subject of the sentence is missing...

is it a bug? Did i do something wrong?

greetings,
andreas