When accessing:
https://domain.com/wp-admin/admin.php?page=gf_entries
The Edit columns button is:
http://domain.com/?gf_page=select_columns&id=3&TB_iframe=true&height=365&width=600
(it should be https://... )
Which breaks the SSL (padlock broken) and doesn't allow and changes to be saved in the field columns.
We administer many sites with SSL support in the backend, this bug is affecting every one of them.
Fix: address url's with this method to instantly work on http and https http://paulirish.com/2010/the-protocol-relative-url/