Why is Dilbert cached?

I keep getting old "Dilberts" with my squid v 1.1.20.
The headers of the document are:

   <META HTTP-EQUIV="expires" CONTENT="Tue, 31 Dec 1996 01:23:45 GMT">
   <META HTTP-EQUIV="Pragma" CONTENT="no-cache">

Even so, I still keep getting yesterday's Dilbert using my cache!
I thought "no-cache" and the "expires"-tag would keep it from
getting cached, or at least be refreshed at the next request...

I'm using the default refresh_pattern, because I haven't really
understood how to customize it myself yet...

Could somebody enlighten me, a poor newcomer in the world of
squids and caches in general?

-- 
Roar Pettersen    http://www.link.no/roar/
roar@link.no
Telenor Link AS   http://www.link.no/