Hi there,
Restricted volumes cannot be written or read by client systems - so it never should have worked like that. I did a search of our BURT database and can't see anything fixed that might have allowed it. I feel confident that testing read/write from restricted volumes don't work is part of the system tests we perform before shipping, so I'm not sure what your system was doing before.
This documentation covers the high level management of SMTape via NDMP restores - http://docs.netapp.com/ontap-9/index.jsp?topic=%2Fcom.netapp.doc.dot-cm-ptbrg%2FGUID-A5C726F4-95FD-4DEF-A401-9E4ECA12DA9A.html
If this is still an issue, I would encourage you to raise a case with our support organisation, or the support for your backup management software.
Hope this helps!