About Varnish cache delivery

[FabD [ML]]

Hi,

I've a question about a case :

1) Imagine Varnish have a page in cache, but a page that is not compressed.
2) If I call this page with a client that supports gzip encoding,
varnish ask backend for a gzip encoded page or send the non-encoded
page from cache ?

Actually, i notice sometime I receive some "non-encoded" page, I would
like to understant why.

ps : Accept-encoding header is normalized.

Thanks,
Fabien