My understanding is that the notification bar is "above" all of the on-page content, as though it is some sort of digital venetian blind that covers all the page content below it.
However, I recently discovered this:
It appears that the share-a-link box is attempting to escape from the notification bar's oppressive covering. For me, this qualifies as unexpected behavior. Bug or no bug?
Edit: To clarify, if this occurred when I clicked or hovered over a page element, I might expect the box to pop to the top over the bar. However, when the popup already exists on the page and I scroll down, the share-a-link box suddenly overlapping the notification bar looks "weird."