When I go to my Gallery & select all the photos for say USA, on the right there is a section called 'Related categories'.
When I click 'Me' in that section I get to see everbody's 'ME' pictures.
I was expecting only the photos of me in my gallery in the USA.
Is that a glitch or is that what the expectation is?
Yes, that's as expected. The link goes to the full category. The "+" behind it adds it as a filter to the current selection, so does what you were expecting. (The thing is that drilling down like that surprisingly swiftly ends up with empty categories, so would give a rather jarring experience if it was the default behaviour.)
[ Edit: Edited on 27-Mar-2014, at 10:38 by Sander ]