From the flag website......
"The UK flag is NOT entirely symmetrical! You can rotate the flag and it still will be the right way up but you can't invert it (not refective symmetry)."
Isn't that what I said, they use inverted and I said flipped/reversed.......tomato-tomahto...whatever.
So you can rotate the flag and it's not upside down. but if you flip it top to bottom, it is upside down......
Wow, you guys really know how to make things difficult............
Your example of the US flag is rotated, if it were inverted, the stars would be in the lower left, so it is
upside down either rotated or inverted. Your flag is only upside down when inverted.........now my head hurts.