[Brian]

If you scroll to the very top of your projects, you'll see that the top of the item at the top of the list doesn't touch the bottom of the toolbar: it's got a little bit of breathing room.

While you're scrolling, the headers will stop in that same spot - until the next item gets within a certain distance. Then they yield that spot to the next item and scroll off the top of the screen.

Behaving as intended, in other words. :-)