If NetworkManager creates a new PlatformConfig and then you execute the following code
the proxyConfig does not get serialised to the PlatformConfig file:

ConfigParams advertisement = config.getPlatformConfig();
XMLDocument proxy = (XMLDocument) StructuredDocumentFactory.newStructuredDocument(MimeMediaType.XMLUTF8, "Parm");
proxy.appendChild(proxy.createElement("isOff"));
advertisement.putServiceParam(PeerGroup.proxyClassID, proxy);
config.proxyConfig = proxy;
config.save();