Chatter REST API "/connect/batch" resource to post multiple files

ChatterApiPostMultipleFiles.java

String header = '--some_random_boundary_string' + '\r\n';
String separator = '\r\n' + '--some_random_boundary_string' + '\r\n';
String footer = '\r\n' + '\r\n' + '--some_random_boundary_string--';

HttpRequest req = new HttpRequest();
req.setEndpoint( URL.getSalesforceBaseUrl().toExternalForm() + '/services/data/v39.0/connect/batch');
req.setHeader('Authorization', 'OAuth ' + UserInfo.getSessionId());
req.setHeader('Content-Type', 'multipart/form-data; boundary=some_random_boundary_string');
req.setHeader('Accept', 'application/json');
req.setBody(header +
            'Content-Disposition: form-data; name="json"' + '\r\n' +
            'Content-Type: application/json' + '\r\n' + '\r\n' +
            '{ "haltOnError" : true, "batchRequests" : [' +
                '{ "url": "/v39.0/connect/files/users/me", "method":"POST", "binaryPartName":"binaryPart1", "binaryPartNameAlias":"fileData" },' +
                '{ "url": "/v39.0/connect/files/users/me", "method":"POST", "binaryPartName":"binaryPart2", "binaryPartNameAlias":"fileData" }' +
            ']}' + '\r\n' + '\r\n' +
            separator +
            'Content-Disposition: form-data; name="binaryPart1"; filename="FileA.txt"' + '\r\n' +
            'Content-Type: application/octet-stream; charset=ISO-8859-1' + '\r\n' +
            'Content-Transfer-Encoding: binary' + '\r\n'  + '\r\n' +
            'aaa' + // content for FileA
            separator +
            'Content-Disposition: form-data; name="binaryPart2"; filename="FileB.txt"' + '\r\n' +
            'Content-Type: application/octet-stream; charset=ISO-8859-1' + '\r\n' +
            'Content-Transfer-Encoding: binary' + '\r\n'  + '\r\n' +
            'bbb' + // content for FileB
            footer
);
req.setMethod('POST');
req.setTimeout(60000);

HttpResponse res = new Http().send( req );

System.debug( res );
System.debug( res.getBody() );

Seems to be a bug with this API where the binaryPartNameAlias is not being processed
http://salesforce.stackexchange.com/questions/164606/chatter-rest-batch-post-multiple-files-missing-expected-filedata-binary-param