The dumpObject control causes a ClassCastException (e.g. "java.lang.Integer incompatible with java.lang.String") when attempting to dump the contents of a TreeMap (and presumably other SortedMaps).
The immediate cause is in the renderer class com.ibm.xsp.extlib.renderkit.html_extended.misc.DumpObjectRenderer, line 443, which attempts to get a property from the map wrapper using a .toString()'d version of the key:
Object o = it.next();
String key = o.toString();
// ...
Object value = a.getProperty(key);
This causes an exception with Maps with keys not comparable with String. A quick fix that worked in my limited testing is to change that line to instead use the original, non-converted key "o":
Object value = a.getProperty(o);