[I guess this bug is in netconf-connector, but such component is missing from Bugzilla's drop-down list.]

Minor severity, as instead of deleting a service directly, one can delete the backing module instead.

On Helium build, after
feature:install odl-bgpcep-all odl-restconf-noauth odl-netconf-connector-all
there is "example-ipv6-topology" service doing basically nothing:

curl -H "Accept:application/json" 127.0.0.1:8181/restconf/config/opendaylight-inventory:nodes/node/controller-config/yang-ext:mount/config:services/service/odl-topology-api-cfg:topology-reference/instance/example-ipv6-topology
returns:
{"instance":[

]}

(There is also example-ipv4-topology item we want to keep.)

Here is an attempt to delete example-ipv6-topology:
curl -v -X DELETE 127.0.0.1:8181/restconf/config/opendaylight-inventory:nodes/node/controller-config/yang-ext:mount/config:services/service/odl-topology-api-cfg:topology-reference/instance/example-ipv6-topology
returns:

• About to connect() to 10.25.2.9 port 8181 (#0)
• Trying 10.25.2.9...
• connected
• Connected to 10.25.2.9 (10.25.2.9) port 8181 (#0)
  > DELETE /restconf/config/opendaylight-inventory:nodes/node/controller-config/yang-ext:mount/config:services/service/odl-topology-api-cfg:topology-reference/instance/example-ipv6-topology HTTP/1.1
  > User-Agent: curl/7.27.0
  > Host: 10.25.2.9:8181
  > Accept: /
  >
  < HTTP/1.1 500 Server Error
  < Content-Type: application/json
  < Transfer-Encoding: chunked
  < Server: Jetty(8.1.14.v20131031)
  <
  {
  "errors": {
  "error": [
  {
  "error-type": "application",
  "error-tag": "operation-failed",
  "error-message": "Error while deleting data",
  "error-info": "java.lang.RuntimeException: RemoteDevice {controller-config}: Error while deleting /(urn:opendaylight:params:xml:ns:yang:controller:config?revision=2013-04-05)services/service/service[{(urn:opendaylight:params:xml:ns:yang:controller:config?revision=2013-04-05)type=(urn:opendaylight:params:xml:ns:yang:controller:topology?revision=2013-11-15)topology-reference}]/instance/instance[{(urn:opendaylight:params:xml:ns:yang:controller:config?revision=2013-04-05)name=example-ipv6-topology}]\n\tat org.opendaylight.controller.sal.connect.netconf.sal.tx.NetconfDeviceWriteOnlyTx.delete(NetconfDeviceWriteOnlyTx.java:161)\n\tat
  (and many lines more)
  
  
  Here is an interesting part of karaf.log file:
  2015-01-20 16:45:58,729 | WARN | oupCloseable-4-4 | NetconfDeviceCommunicator
  | 242 - org.opendaylight.controller.sal-netconf-connector - 1.1.2.SNAPSHOT | RemoteDevice{controller-config}

  : Error reply from remote device, request: <rpc message-id="m-100" xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
  <edit-config>
  <target>
  <candidate/>
  </target>
  <default-operation>none</default-operation>
  <config>
  <services xmlns="urn:opendaylight:params:xml:ns:yang:controller:config">
  <service>
  <type xmlns:x="urn:opendaylight:params:xml:ns:yang:controller:topology">x:topology-r
  eference</type>
  <instance xmlns:a="urn:ietf:params:xml:ns:netconf:base:1.0" a:operation="delete">
  <name>example-ipv6-topology</name>
  </instance>
  </service>
  </services>
  </config>
  </edit-config>
  </rpc>
  , response: <rpc-reply xmlns="urn:ietf:params:xml:ns:netconf:base:1.0" message-id="m-100">
  <rpc-error>
  <error-type>application</error-type>
  <error-tag>invalid-value</error-tag>
  <error-severity>error</error-severity>
  <error-message>One element provider expected in XmlElement

  {name='instance', namespace='urn:opendaylight:params:xml:ns:yang:controller:config'}

  </error-message>
  </rpc-error>
  </rpc-reply>

NetconfDocumentedException{message=One element provider expected in XmlElement

, errorType=application, errorTag=invalid_value, errorSeverity=error, errorInfo=null}
at org.opendaylight.controller.netconf.api.NetconfDocumentedException.fromXMLDocument(NetconfDocumentedException.java:245)

It looks like RPC has delete operation on 'instance' list, instead of just 'example-ipv6-topology' item.
Am I doing something wrong or is this really a bug?