[squid-users] warning "This cache hit is still fresh and more than 1 day old"

sometimes wget something that is already cached gets a warning "This
cache hit is still fresh and more than 1 day old".
What causes this?

Also a while ago, I complained about unValidated objects in cache.conf
The above warning seems to be the reason behind those unvalidated
objects.

For example, if it says 530420 Objects loaded but Validated 530419
Entries, the 1 object that failed validation is the one that gives "This
cache hit is still fresh and more than 1 day old" warning.
using squidclient to PURGE that one entry from cache, removes the
unvalidated entry.
I can tell which is the unvalidated entry because when it gets request
again, a SWAP_FAIL is logged in access.log

I am using the default refresh patterns.
What causes "This cache hit is still fresh and more than 1 day old"
warnings?

thank you.