First, staff users on sites not using mezzanine.core.middleware.SitePermissionMiddleware without explicitly defined sitepermissions will cause RelatedObjectDoesNotExist bugs.
I've put in a pull request to mezzanine (https://github.com/stephenmcd/mezzanine/pull/1501) which if accepted will fix the first issue. The best fix for the second issue will depend on whether the pull request is merged in.
Since https://github.com/stephenmcd/mezzanine/commit/d5d21ba527bd417de956cc1f768d98ca7f851c13 sitepermissions aren't guaranteed to exist. This creates a couple potential problems.
First, staff users on sites not using
mezzanine.core.middleware.SitePermissionMiddlewarewithout explicitly defined sitepermissions will causeRelatedObjectDoesNotExistbugs.Second, the MultiSiteCalloutAdmin (https://github.com/fusionbox/django-widgy/blob/master/widgy/contrib/widgy_mezzanine/admin.py#L347) assumes all users have sitepermissions.
I've put in a pull request to mezzanine (https://github.com/stephenmcd/mezzanine/pull/1501) which if accepted will fix the first issue. The best fix for the second issue will depend on whether the pull request is merged in.