[squid-users] Revalidation question

Hi all,

We are using 2.5STABLE3 and have found some unexpected (to us, anyway)
re-validation behavior.

If we have document fetched from the source server with no expires header,
bring the source server down, and then attempt to fetch that document from
Squid with an "if-modified-since" request header, then Squid will return the
document with a 200 OK response header and no indication that the source
server is down. Turning up the debug logs shows that Squid is attempting
to connect to the source server and failing; it also appears to be
constructing a response that contains an X-Squid-Error header, but this
response seems to be discarded in favor of the 200/OK response actually
received by the client.

Is this a bug, or expected behavior? If this is expected behavior, can
someone please point me to whatever spec indicates that this is expected
behavior? Is there a config parameter somewhere that we are missing?

Thanks in advance,
Michael