Clustering : random "Error creating data" when writing flows to config DS

I tried to POST xml files from integration test suite. I randomly ran into error described in next text. When I try to POST same data right away after receiving error POST succeeds. I was not able to trace any log data in karaf.log. This seems to be one of reasons of failing robot tests.

martin@ncc1701e:~/programs/odlRestyScripts$ POST < /integration/test/csit/variables/xmls//f7.xml
{"errors":{"error":[

{"error-type":"application","error-tag":"operation-failed","error-message":"Error creating data"}

]}}
martin@ncc1701e:~/programs/odlRestyScripts$ POST < /integration/test/csit/variables/xmls//f9.xml
{"errors":{"error":[

{"error-type":"application","error-tag":"operation-failed","error-message":"Error creating data"}

]}}
martin@ncc1701e:~/programs/odlRestyScripts$ POST < /integration/test/csit/variables/xmls//f11.xml
{"errors":{"error":[

{"error-type":"application","error-tag":"operation-failed","error-message":"Error creating data"}

]}}