I am using Build 10586 .. this is a bug .. swiping up in the nav bar should hide it doesn't matter what are doing .. But it seems to work only when you enable screen lock on double tapping the NAV Bar .. (( Happens when playing xbox games & some apps even though the apps support windows 10, Yes Your apps has to support windows 10 or there remains a black holo space where the navigation bar is supposed to be))
Go to Settings > Personalization > Lock Screen > Enable "Double tab the Navigation bar to turn off the screen"
Now what I did was , double clicked on Navigation bar & it locked the screen .. then I instinctively swiped up on the nav bar after unlocking .. and
Full immersive mode was active . ..
NOW Disabling "Double tab the Navigation bar to turn off the screen" function doesn't seem to disable full immersive mode on swipe ..
The first thing i thought was to help others sharing the solution .. as I found none on the internet searching for about 2 days ..