rdf schema broken with trang?

If I take 
http://www.w3.org/TR/2003/WD-rdf-syntax-grammar-20030123/rdfxml.rng 
(which is in fact a compact syntax file, despit the rng suffix)
and convert it to RNG, and then convert it back, I get an error from trang:

[spqr-ibm]/TEI/P5/Test:trangs rdfxml.rng test.rnc
Exception in thread "main" java.lang.NullPointerException
        at com.thaiopensource.relaxng.output.rnc.Output.encode(Unknown 
Source)
        at 
com.thaiopensource.relaxng.output.rnc.Output.encodedText(Unknown Source)
        at 
com.thaiopensource.relaxng.output.rnc.Output.access$1900(Unknown Source)
        at 
com.thaiopensource.relaxng.output.rnc.Output$NameClassOutput.visitNsName(Unknown 
Source)
        at 
com.thaiopensource.relaxng.edit.NsNameNameClass.accept(Unknown Source)
        at 
com.thaiopensource.relaxng.output.rnc.Output$NameClassOutput.visitChoice(Unknown 
Source)
        at 
com.thaiopensource.relaxng.edit.ChoiceNameClass.accept(Unknown Source)
        at 
com.thaiopensource.relaxng.output.rnc.Output$NameClassOutput.visitAnyName(Unknown 
Source)
        at 
com.thaiopensource.relaxng.edit.AnyNameNameClass.accept(Unknown Source)
        at 
com.thaiopensource.relaxng.output.rnc.Output$PatternOutput.nameClassed(Unknown 
Source)
        at 
com.thaiopensource.relaxng.output.rnc.Output$PatternOutput.visitElement(Unknown 
Source)
        at com.thaiopensource.relaxng.edit.ElementPattern.accept(Unknown 
Source)
        at 
com.thaiopensource.relaxng.output.rnc.Output$ComponentOutput.visitDefine(Unknown 
Source)
        at 
com.thaiopensource.relaxng.edit.DefineComponent.accept(Unknown Source)
        at 
com.thaiopensource.relaxng.output.rnc.Output.innerBody(Unknown Source)
        at com.thaiopensource.relaxng.output.rnc.Output.topLevel(Unknown 
Source)
        at com.thaiopensource.relaxng.output.rnc.Output.output(Unknown 
Source)
        at 
com.thaiopensource.relaxng.output.rnc.RncOutputFormat.outputPattern(Unknown 
Source)
        at 
com.thaiopensource.relaxng.output.rnc.RncOutputFormat.output(Unknown Source)
        at com.thaiopensource.relaxng.translate.Driver.doMain(Unknown 
Source)
        at com.thaiopensource.relaxng.translate.Driver.main(Unknown Source)


Any suggestions? an error in trang, or an error in the schema?

Sebastian Rahtz

PS why do I want to do this? because I want to include the RDF in my own 
XML syntax schema,
and then convert the whole shebang to RNC