Rule disappears from Form Customization but not from the database

dae created Redmine issue ID 2639

Steps to reproduce:
# Go to "Form Customization".
# Click "Add", create a new rule, save.
# Edit the newly created rule: change "Action" to "No action", click Save.

What happens: the rule disappears from the list, but you can still see it in the database (table _modx_actiondom_).
