25 September 2013 at 1:49am
I had the same problem: SS3.1 with the latest master version of Userforms from Github (today) and the Form tab was showing up blank.
I did a flush on the actual page in the CMS and it returned. eg. /admin/pages/edit/show/3?flush=1
A normal flush on /admin wasn't enough, it had to be on the actual/specific page.