space scrolls the entire page down, and shiftspace scrolls the entire page back up as expected. Note that in particular, this means you can use shiftspace to scroll the subject back into view without using the mouse.
Previous behavior (if I recall correctly):
space would scroll the content within the div down, but not the entire page. Upon reaching the end of the content, it would start scrolling the content back up.
The current behavior confirmed above seems more standard/expected, and allowing me to scroll the subject back into view without using the mouse is very welcome.
It still seems annoying from a UX point of view that the subject ever scrolls off the screen, though.