Re: Rules for combining headers in a caching proxy...

! response.  The end-to-end headers stored in the cache entry are used
! for the constructed response, except that any end-to-end headers
! provided in the 304 response MUST replace the corresponding headers
! from the cache entry.  Unless the cache decides to remove the cache
! entry, it MUST also replace the end-to-end headers stored with the
! cache entry with corresponding headers received in the incoming response.

I won't speak for anyone else, but that works for me.  Thanks.

rst