ArrayIndexOutOfBoundsException in luindex performance runs

I've seen this twice so far. http://jikesrvm.anu.edu.au/cattrack/results/habanero.anu.edu.au/perf/5279/production/default/perf-dacapo/luindex-10

It's intermittent, appears to be new within the last week. Suggest we monitor for a few more days to see if it shakes out on its own or if it needs investigation.

Stack trace from output appended.

java.lang.ArrayIndexOutOfBoundsException: 21 >= 3
java.lang.ArrayIndexOutOfBoundsException: 21 >= 3
at .<invisible method>(Unknown Source:0)
at java.lang.VMThrowable.fillInStackTrace(VMThrowable.java:49)
at java.lang.Throwable.fillInStackTrace(Throwable.java:498)
at java.lang.Throwable.<init>(Throwable.java:159)
at java.lang.Exception.<init>(Exception.java:78)
at java.lang.RuntimeException.<init>(RuntimeException.java:76)
at java.lang.IndexOutOfBoundsException.<init>(IndexOutOfBoundsException.java:73)
at java.lang.ArrayIndexOutOfBoundsException.<init>(ArrayIndexOutOfBoundsException.java:75)
at java.util.Vector.raiseBoundsError(Vector.java:934)
at java.util.Vector.checkBoundExclusive(Vector.java:921)
at java.util.Vector.elementAt(Vector.java:391)
at org.apache.lucene.store.RAMOutputStream.flushBuffer(RAMOutputStream.java:82)
at org.apache.lucene.store.BufferedIndexOutput.flush(BufferedIndexOutput.java:84)
at org.apache.lucene.store.BufferedIndexOutput.close(BufferedIndexOutput.java:99)
at org.apache.lucene.store.RAMOutputStream.close(RAMOutputStream.java:97)
at org.apache.lucene.index.TermInfosWriter.close(TermInfosWriter.java:142)
at org.apache.lucene.index.DocumentWriter.writePostings(DocumentWriter.java:366)
at org.apache.lucene.index.DocumentWriter.addDocument(DocumentWriter.java:112)
at org.apache.lucene.index.IndexWriter.addDocument(IndexWriter.java:450)
at org.apache.lucene.index.IndexWriter.addDocument(IndexWriter.java:436)
at dacapo.luindex.LuindexHarness.indexDocs(LuindexHarness.java:122)
at dacapo.luindex.LuindexHarness.indexDocs(LuindexHarness.java:116)
at dacapo.luindex.LuindexHarness.indexDocs(LuindexHarness.java:116)
at dacapo.luindex.LuindexHarness.iterate(LuindexHarness.java:82)
at dacapo.Benchmark.run(Benchmark.java:126)
at dacapo.TestHarness.runBenchmark(TestHarness.java:301)
at dacapo.TestHarness.main(TestHarness.java:242)
at Harness.main(Harness.java:5)