Sticky was working fine until I removed the promo bar at the header-top section, leaving the header-top empty, and using only header-main and header-bottom with items in it.
What ends up happening is that when you scroll down, sticky-on class appears as expected on header-main and bottom. But when scrolling up, header-top sticky-on disappears as expected, but header-bottom sticky-on stays in place.
The only fix is if I put something in the header-top then everything works. This has happened on my dev site as well as 3 fresh installs (one on a completely different server).
EDIT: Forgot to mention that it seemed to only be happening on Chrome. Safari was fine.