Hi Donald,
thanks for your advise, I finally got it solved.
The problem was caused by prefixes in the PUT request body ( copied that from the web UI trace).
After removing the "prefixes" node the links are created in both CCM and QM.
================= successful PUT sequence ===============
>> put(1) https:/myhost/qm/proxy?uri=https%3A%2F%2Fm5l.oc1232020505.ibm.com%3A9443%2Fccm%2Fresource%2FitemName%2Fcom.ibm.team.workitem.WorkItem%2F167%3Foslc.properties%3Doslc_cm%3ArelatedTestCase
>> Request Headers:
- Accept application/json
- Content-Type application/json
- OSLC-Core-Version 2.0
- Accept-Language en-US,en;q=0.5
- Accept-Encoding gzip, deflate, br
- X-Jazz-CSRF-Prevent 0000v6WP8CUG5l6R5nBF6thGY6D:3adf14e3-b466-4eab-9d71-2886d8dbc600
>> content
{"oslc_cm:relatedTestCase": [{
"rdf:resource": "https:/myhost/qm/oslc_qm/contexts/GuNbAFS5EeeMvZ59-cIRUA/resources/com.ibm.rqm.planning.VersionedTestCase/_iN7gMV_VEeelX9MkB83u9A",
"dcterms:title": "350: DOM4-S24B#KP"
}]}
>> Response Headers:
- X-Powered-By Servlet/3.0
- x-com-ibm-team-scenario 172.16.9.1
- X-Powered-By Servlet/3.0
- x-com-ibm-team-scenario 172.16.9.1
- ETag "44ea77cd-fa82-387f-b25f-8b1a67cfe7e7"
- Last-Modified Thu, 20 Jul 2017 16:12:28 GMT
- Expires Thu, 20 Jul 2017 16:12:28 GMT
- Vary Accept, OSLC-Core-Version
- Content-Type application/json;charset=UTF-8
- Content-Language en-US
- Date Thu, 20 Jul 2017 16:12:28 GMT
- Cache-Control private, must-revalidate, max-age=0, no-cache=set-cookie
- Content-Length 646
HTTP/1.1 200 OK
>> put(1) https:/myhost/qm/oslc_qm/contexts/_GuNbAFS5EeeMvZ59-cIRUA/resources/com.ibm.rqm.planning.VersionedTestCase/_iN7gMV_VEeelX9MkB83u9A
>> Request Headers:
- Accept application/xml
- Accept-Language en-US,en;q=0.5
- Accept-Encoding gzip, deflate, br
- Content-Type application/rdf+xml
- X-Jazz-CSRF-Prevent 0000v6WP8CUG5l6R5nBF6thGY6D:3adf14e3-b466-4eab-9d71-2886d8dbc600
>> content
<rdf:RDF xmlns:dcterms="http://purl.org/dc/terms/" xmlns:oslc_qm="http://open-services.net/ns/qm#" xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#">
<oslc_qm:TestCase rdf:about="https:/myhost/qm/oslc_qm/contexts/_GuNbAFS5EeeMvZ59-cIRUA/resources/com.ibm.rqm.planning.VersionedTestCase/_iN7gMV_VEeelX9MkB83u9A">
<dcterms:title>DOM4-S24B#KP</dcterms:title>
<oslc_qm:relatedChangeRequest rdf:ID="n0" rdf:resource="https:/myhost/ccm/resource/itemName/com.ibm.team.workitem.WorkItem/167"/>
</oslc_qm:TestCase>
<rdf:Description rdf:about="#n0">
<rdf:type rdf:resource="http://www.w3.org/1999/02/22-rdf-syntax-ns#Statement"/>
<dcterms:title>167: Bug non testés.</dcterms:title>
</rdf:Description>
</rdf:RDF>
>> Response Headers:
- X-Powered-By Servlet/3.0
- x-com-ibm-team-scenario 172.16.9.1
- OSLC-Core-Version 2.0
- ETag "_OiD2Zm1mEeeI6eQTzQW-A"
- Location https:/myhost/qm/oslc_qm/contexts/_GuNbAFS5EeeMvZ59-cIRUA/resources/com.ibm.rqm.planning.VersionedTestCase/_iN7gMV_VEeelX9MkB83u9A
- Content-Language en-US
- Content-Length 0
- Date Thu, 20 Jul 2017 16:12:28 GMT
HTTP/1.1 200 OK