During UX review, I noticed when opening Support>System Information the loading mask appeared at the top of the page rather than in the middle. I'm guessing this is because if in the middle, it'd literally be in the middle which would essentially be unseen 99% of the time because the system information is so long.
I asked Daniel and he replied:
"This is actually the feature loading mask, not the form loading mask. Subtle difference. If you click through some of the other menu items, you’ll notice this mask flashing briefly.
I’d file this anyway, since it should mask the entire content window (including breadcrumb), not just the buttons and body. There might also be a way to center the loading indicator, since I agree it’s weird to have it anchored to the top."
Filing as an improvement, though I suppose it could be a bug too.