Weird behavior when scrolling in expandable grid

This happens when some of the rows are expanded and I try to scroll down. The lower boundary of the rendering list moves up together and eventually moves out of view.

The behavior can be replicated in the ui-grid tutorial page.

1. Go to http://ui-grid.info/docs/#/tutorial/216_expandable_grid
2. Expand all on any demo grid at the bottom of the page.
3. Scroll down

Screen shot before expand:

After expand and scrolling:

Notice that it ends at row 18 while expanded but it's not the last item in the list.