CSS Validation error

To whom it may concern,
I had a question concerning your validation process concerning CSS files and
the false positives its returning (at least I hope this is the case)
the syntax:
filter:progid.dximagetransform.microsoft.insertfilterhere(properties of said
filter);} is coming back as invalid by saying it does not exist and after
having exhaustively checked and rechecked with various respected authorities
on proper
usage of CSS, filters and said elements the only source of falsehood seems
to be your
validation tool located at:
http://jigsaw.w3.org/css-validator/#validate_by_upload
Is this my mistake or yours? It said my options were to either remove it, or
live with it being invalid? That's a bit arrogant, do you not think? Since
yours is the only source claiming this as illegitimate syntax within CSS
files, but I could be wrong.