Hi Jeff,
In my code I'm using OpenCMIS based URL and I'm using 4.2.c
In my code I'm not overwriting property. First I'm creating folder and then document. Below is the code - 
Folder root = session.getRootFolder();
        Map<String, Object> folderProperties = new HashMap<String, Object>();
        String foldername="testfolder";
        folderProperties.put(PropertyIds.OBJECT_TYPE_ID, "cmis:folder");
        folderProperties.put(PropertyIds.NAME, foldername);
 Folder  newFolder = root.createFolder(folderProperties);
        Map<String, Object> contentProperties = new HashMap<String, Object>();
        contentProperties.put(PropertyIds.OBJECT_TYPE_ID, "cmis:document,P:cm:titled");
        contentProperties.put(PropertyIds.NAME, "TestName");
        contentProperties.put("cm:description", "Test");
         byte[] content = " Testdata".getBytes();
        InputStream stream = new ByteArrayInputStream(content);
        ContentStream contentStream = new ContentStreamImpl(name, new BigInteger(content), "text/plain", stream);
       Document document =  newFolder.createDocument(contentProperties, contentStream, VersioningState.MINOR);
Error: 
org.apache.chemistry.opencmis.commons.exceptions.CmisObjectNotFoundException: Type 'cmis:document,P:cm:titled' is unknown!
   at org.apache.chemistry.opencmis.client.bindings.spi.atompub.AbstractAtomPubService.convertStatusCode(AbstractAtomPubService.java:432)
   at org.apache.chemistry.opencmis.client.bindings.spi.atompub.AbstractAtomPubService.read(AbstractAtomPubService.java:554)