I'm baffled. Would it be possible for you to send a scaled down (but compilable) version of your response writer that demonstrates the problem, along with a snippet that can be added to the example solrconfig.xml to register it and and example request URL that triggers the problem?
that way we can all try ait and see if we can reproduce your results (for all we know, it may be an artifact of your debugger) -Hoss
