HttpWebRequest returned with deprecated resource, although cache control has max-stale 0

Given that it HttpWebRequestperforms a GET with the URL c Cache-Control max-stale=0, and the server returns the resource c max-age=900, why would the returned one HttpWebResponsehave IsFromCache=truealong with the warning header that the response is out of date

The response stream contains the payload received from the client Temporary Internet Fileswhen the server side has a newer version of the available resource. More than 900 seconds have passed since the local cache was populated.

I also noticed that the result of this was mixed. The same code executed twice sometimes returns an obsolete resource and sometimes returns an updated resource. When an updated resource returns, it does not update the cache Temporary Internet Files.