FYI, in iOS9 in safari tapping the 2 square Icon opens a menu, that allows you to tap the private icon.
It will remember that forever until you change it ! (persists thru rebooting/upgrading)
You can tell you are in private more if the top address/search bar is dark gray.
Its not obvious unless you *know* this. (Apparently i have been in Private mode for a while ...)
For me.with Private on, if i browse to a Nettalk site, my ajax /send to server stuff does not work.
So my loginform just sits there dumb like,
But, if you toggle out of private mode and access the page it will work!.
i thought Private was about browser history,
but it seem to have additional side effects on my NT sites.
I believe it is blocking some of the cookie tracking.