XMI Serialization of replies is not checking for FS references when serializing incoming FSs

As discovered by Matthias Wendt when the incoming FS has a feature with multiple references which is set by the C++ annotator, the FS reference is not serialized.
Mathias provided the sample XMI below returned in the reply from a C++ service where the 'variant' feature gets an id-ref value of "4", but there is no object having xmi:id="4".
The feature 'variant' has MultipleReferenceAllowed set to true. The encompassing FS is passed to C++ annotator which sets the 'variant' feature.

....(.........................n....K[..........$..T,...2....<?xml version
="1.0" encoding="UTF-8"?><xmi:XMI xmlns:examples="http:///org/apache/uima/e
xamples.ecore" xmlns:cas="http:///uima/cas.ecore" xmlns:tcas="http:///uima/
tcas.ecore" xmlns:xmi="http://www.omg.org/XMI" xmi:version="2.0"><cas:NULL
xmi:id="0"/> <cas:Sofa xmi:id="1" sofaNum="1" sofaID="_InitialView" mimeTy
pe="text" sofaString="Load or edit text here."/>. <tcas:DocumentAnnotation
xmi:id="2" sofa="1" begin="0" end="23" language="en"/>. <examples:David xmi
:id="3" sofa="1" begin="0" end="1" variants="4"/>.<cas:View sofa="1" member
s="2 3"/></xmi:XMI>....9......CasReference...-37f4a0fc:124c9361c79:-7feb..C
ommand.......IdleTime.......?...MessageFrom...DAVEDETECTORQ..MessageType...
....Payload.......ServerURI...tcp://localhost:61616..TimeInAnalytic........
`..TimeInProcessCAS........`..TimeInService...........TimeToDeserializeCAS.
.......P..TimeToSerializeCAS...................