You have to be logged into github and have access to aspnetzero for those links to work.
It only happens on a modal window after you make a selection from a lookup (Pick).
On the screenshot above: The first time you open the modal, the scrollbar is visible and works. As soon as you make a selection (for example category lookup), the scrollbar disappear and you can longer scroll.
Thanks,
Ed
I am having the same issue with jquery.
You can use the bootstrap grid system:
