On the first public beta I can only rarely get pull to refresh, the default seems to be it not working as opposed to your experience. Killing the app and rebooting both don't fix the behavior. Occasionally going into landscape mode will enable pull to refresh for a single use and then it will stop working again.
same for me. installed b5 on an ipad and iphone and pull to refresh doesn't work if the list of feed folders is short enough to not extend below the crease. if I expand a category folder to reveal the enclosed feeds and to extend the list below the crease, the refresh will work again. then will stop working if i collapse the folder again.