Strange event receiver behaviour

Here is the relevant code (it's almost identical for all 3) in case the issue is here.

public override void ItemDeleting(SPItemEventProperties properties)
        {
            base.ItemDeleting(properties);
            using (SPSite site = new SPSite(properties.WebUrl))
            {
                using (SPWeb web = site.OpenWeb())
                {
                    int _currentUser = properties.CurrentUserId;
                    SPUser spCurrentUser = web.SiteUsers.GetByID(_currentUser);
                    if (spCurrentUser.IsSiteAdmin == true)
                    {
                        properties.Cancel = false;
                        properties.Status = SPEventReceiverStatus.Continue;
                    }
                    else
                    {
                        properties.Cancel = true;
                        properties.ErrorMessage = "Past registrations can only be deleted by a site administration";
                    }

                }
            }