ConcurrentModificationException in MemorySearchProvider

I get this error during normal use of WIAB (using trunk):

INFO: Submit to [WaveletName localhost/w+o8UvbYIRZeA/localhost/conv+root] by vjrj@localhost @ 0 with 4 ops
2012-02-09 02:16:55.289:WARN:oejs.ServletHandler:/search/
java.util.ConcurrentModificationException
at java.util.HashMap$HashIterator.nextEntry(HashMap.java:810)
at java.util.HashMap$EntryIterator.next(HashMap.java:851)
at java.util.HashMap$EntryIterator.next(HashMap.java:849)
at com.google.common.collect.AbstractMultimap$KeySet$1.next(AbstractMultimap.java:902)
at org.waveprotocol.box.server.waveserver.MemorySearchProvider.filterWavesViewBySearchCriteria(MemorySearchProvider.java:166)
at org.waveprotocol.box.server.waveserver.MemorySearchProvider.search(MemorySearchProvider.java:113)
at org.waveprotocol.box.server.robots.operations.SearchService.search(SearchService.java:72)
at org.waveprotocol.box.server.robots.operations.SearchService.execute(SearchService.java:62)
at org.waveprotocol.box.server.robots.util.OperationUtil.executeOperation(OperationUtil.java:184)
at org.waveprotocol.box.server.rpc.SearchServlet.performSearch(SearchServlet.java:189)
at org.waveprotocol.box.server.rpc.SearchServlet.doGet(SearchServlet.java:170)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:617)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
at org.eclipse.jetty.servlet.ServletHolder.handle(ServletHolder.java:558)
at org.eclipse.jetty.servlet.ServletHandler.doHandle(ServletHandler.java:489)
at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:119)
at org.eclipse.jetty.security.SecurityHandler.handle(SecurityHandler.java:520)
at org.eclipse.jetty.server.session.SessionHandler.doHandle(SessionHandler.java:233)
at org.eclipse.jetty.server.handler.ContextHandler.doHandle(ContextHandler.java:972)
at org.eclipse.jetty.servlet.ServletHandler.doScope(ServletHandler.java:417)
at org.eclipse.jetty.server.session.SessionHandler.doScope(SessionHandler.java:192)
at org.eclipse.jetty.server.handler.ContextHandler.doScope(ContextHandler.java:906)
at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:117)
at org.eclipse.jetty.server.handler.HandlerWrapper.handle(HandlerWrapper.java:110)
at org.eclipse.jetty.server.Server.handle(Server.java:346)
at org.eclipse.jetty.server.HttpConnection.handleRequest(HttpConnection.java:442)
at org.eclipse.jetty.server.HttpConnection$RequestHandler.headerComplete(HttpConnection.java:910)
at org.eclipse.jetty.http.HttpParser.parseNext(HttpParser.java:565)
at org.eclipse.jetty.http.HttpParser.parseAvailable(HttpParser.java:217)
at org.eclipse.jetty.server.AsyncHttpConnection.handle(AsyncHttpConnection.java:46)
at org.eclipse.jetty.io.nio.SelectChannelEndPoint.handle(SelectChannelEndPoint.java:545)
at org.eclipse.jetty.io.nio.SelectChannelEndPoint$1.run(SelectChannelEndPoint.java:43)
at org.eclipse.jetty.util.thread.QueuedThreadPool.runJob(QueuedThreadPool.java:598)
at org.eclipse.jetty.util.thread.QueuedThreadPool$3.run(QueuedThreadPool.java:533)
at java.lang.Thread.run(Thread.java:679)
2012-02-09 02:16:55.289:DBUG:oejs.ServletHandler:[GET /search/?query=in:inbox&index=0&numResults=20]@1686674510 org.eclipse.jetty.server.Request@64889c4e