context level setting is ok, it'll override server/vhost level setting.
cache policy refer following settings:
Cache Request with Cookie
Cache Response with Cookie
Ignore Request Cache-Control
Ignore Response Cache-Control
Enable Private Cache
hmm... it looks like missing one setting:
Cache Request with Query String
will report to development.
as a workaround, please set vhost level
Cache Request with Query String:Yes
see if works.