PD4ProgressListener fails to work

When using multiple source documents, the PD4ProgressListener fails to work. The document is rendered correctly, but the monitoring doesn’t.

This is the progressUpdate method in my listener.

public void progressUpdate(int mID, int prog, String notes, long ms) {
if (DEBUG) Log.theLog.log("~~~~ %s%% Complete", prog);
switch(mID) {
case CONVERSION_BEGIN:
if (DEBUG) Log.theLog.log("~~~~ Conversion Begin");
break;
case HTML_PARSED:
if (DEBUG) Log.theLog.log("~~~~ HTML Parsed");
break;
case DOC_TREE_BUILT:
if (DEBUG) Log.theLog.log("~~~~ Doc Tree Built");
break;
case HTML_LAYOUT_IN_PROGRESS:
if (DEBUG) Log.theLog.log("~~~~ HTML Layout In Progress");
break;
case HTML_LAYOUT_DONE:
if (DEBUG) Log.theLog.log("~~~~ HTML Layout Done");
break;
case TOC_GENERATED:
if (DEBUG) Log.theLog.log("~~~~ TOC Generated");
break;
case DOC_OUTPUT_IN_PROGRESS:
if (DEBUG) Log.theLog.log("~~~~ Doc Output In Progress");
break;
case NEW_SRC_DOC_BEGIN:
if (DEBUG) Log.theLog.log("~~~~ New Src Doc Begin");
break;
case CONVERSION_END:
if (DEBUG) Log.theLog.log("~~~~ Conversion End");
break;
}
}

This is how I am calling it

String html = "<span>Hello world</span>";
StringReader sr = new StringReader(html);
OutputStream os = new ByteArrayOutputStream();

PD4ML pd4ml = new PD4ML();
pd4ml.enableDebugInfo();
pd4ml.useTTF( "java:", true );
pd4ml.setHtmlWidth(1050);
pd4ml.enableSmartTableBreaks(true);

// ResumePrinterQueue.newListener() returns a vanilla PD4ProgressListener
PD4ProgressListener prog = ResumePrinterQueue.newListener();
pd4ml.monitorProgress(prog);

try {
//pd4ml.render(sr, os);  //<
<hr class="bbcode_rule" />
OK

//pd4ml.render(sr, os, new java.net.URL(RTiClient.URL())); //<
<hr class="bbcode_rule" />
OK

StringReader[] arr = {sr};
pd4ml.render(arr, os, new java.net.URL(RTiClient.URL()));  //<
<hr class="bbcode_rule" />
Fails
} catch (Exception e) { }

// Just something to make sure the compiler doesn't throw anything away
Log.theLog.log(new String(((ByteArrayOutputStream)os).toByteArray()).substring(0, 8));

I’m using 3.80fx6 Volume, so I don’t think it is an issue of not having access to the methods. Is there some kind of config flag I am not setting, or is the monitoring broken for this instance?