Checked out my gallery on a Nexus 7 and realized that the bottom navigation bar is NOT hiding automatically after the set time after you have navigated to a second image.
To see what I mean, go to here:
http://www.marinhomephotography.com/gallery/
On the FIRST photo you view, the nav bar WILL auto hide itself.
But if you use the next arrow to navigate to another photos, on the second photo the nav bar will NOT hide itself.
Again, this was on a Nexus 7 using Android 4 something-or-other.
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P.S: I am using prettybox style. As per my other support question, i can’t change to a different style.