Real problem caused by CSS validators willingness to tacitly accept HTML

Dear CSS Validator Team -- I am sure I have mentioned
this before, but today the problem has caused us major
difficulties and considerable wasted time : I would
therefore really appreciate it if it could be resolved
promptly.

Scenario (simplified) :

1) The CSS validator is asked to validate a non-existent CSS page

	http://jigsaw.w3.org/css-validator/validator?uri=http://www.rhul.ac.uk/resources/Stylesheets/CSS/TP-Common.css

2) The CSS Validator says that validation was successful, and
	displays the CSS.

3) The CSS looks /remarkably/ like the CSS that would have
	been found had the URL been specified correctly,
	but with subtle differences that cause massive
	confusion.

Background :

	The IIS is configured to serve a custom 404 (HTML) web
	page on encountering a 404, and this page page links
	to a subtly different version of the CSS file intended
	to be specified at (1) above.  This behaviour has
	now been changed to simplify urgent work here; it
	may be re-instated in due course, but attempts to
	replicate the problem will currently shew very different
	CSS between

	http://jigsaw.w3.org/css-validator/validator?uri=http://www.rhul.ac.uk/resources/Stylesheets/CSS/TP-Common.css

			and

	http://jigsaw.w3.org/css-validator/validator?uri=http://www.rhul.ac.uk/resources/Style-sheets/CSS/TP-Common.css


Results : complete confusion.

Request : could the CSS validator /please/ report (very
	loudly !) if the returned resource is declared at
	HTTP level to be anything other than "text/css",
	and could it also please report if the served file
	appears not to be CSS but (say) HTML with CSS embedded
	or linked ?

Philip TAYLOR