Hello John,
The failover issue occurs because of the conflicting sapmnt shares.
This is discussed at the item 5 from the SAP note 112266.
In order to make this work, I believe that you would need to use a virtual hostname for the non-clustered system as well.
There is a section about using multiple SAP systems at the same server, at the SAP Installation Guides. I believe that could help in this case.
Regards,
Isaías