Organization network cannot be deleted, because it is in use ?

Using vCD 5.1 and having difficulty deleting the organization network after deleting the vApp that was using it. Code snippet below.

Why would this happen if using the waitForTask(0)?  Thanks for your help.

vapp.delete().waitForTask(0);

AdminOrgVdcNetwork orgVdcNw = AdminOrgVdecNetwork.getOrgVdcNetworkByReference(vcloudClient, admOrgVdcNwRef);

admOrgVdcNw.delete().waitForTask(0);