Notify on document local permissions is not stored

How to reproduce it

1. Create a document;
2. Navigate to "Permissions" tab;
3. Create a new permission to the Administrator;
4. Edit the permission, uncheck "Send an email to notify user" field and click "Update" button;
5. Edit the permission again and see that the "Send an email to notify user" checkbox is still checked.

However, if:

1. Edit the permission again and change the "Right" to something different from what is defined;
2. Uncheck the "Send an email to notify user" field and click "Update" button;
3. Edit the permission again and see that this last modification was stored.