Assert failure/ArrayIndexOutOfBoundsException when using COUNT in MERGE matching clause

s.execute("create table t2(x int)");
s.execute("create table t1(x int)");
s.execute("insert into t2 values 3,4");
s.executeUpdate("merge into t1 using t2 on (t1.x=t2.x) " + 
   "when not matched then insert values (count(*))");

Exception in thread "main" java.sql.SQLException: Java exception: '-1: java.lang.ArrayIndexOutOfBoundsException'.
        at org.apache.derby.impl.jdbc.SQLExceptionFactory.getSQLException(Unknown Source)
        at org.apache.derby.impl.jdbc.SQLExceptionFactory.getSQLException(Unknown Source)
        at org.apache.derby.impl.jdbc.Util.seeNextException(Unknown Source)
        at org.apache.derby.impl.jdbc.Util.javaException(Unknown Source)
        at org.apache.derby.impl.jdbc.TransactionResourceImpl.wrapInSQLException(Unknown Source)
        at org.apache.derby.impl.jdbc.TransactionResourceImpl.handleException(Unknown Source)
        at org.apache.derby.impl.jdbc.EmbedConnection.handleException(Unknown Source)
        at org.apache.derby.impl.jdbc.ConnectionChild.handleException(Unknown Source)
        at org.apache.derby.impl.jdbc.EmbedStatement.execute(Unknown Source)
        at org.apache.derby.impl.jdbc.EmbedStatement.executeLargeUpdate(Unknown Source)
        at org.apache.derby.impl.jdbc.EmbedStatement.executeUpdate(Unknown Source)
        at derby6565.Derby6565.main(Derby6565.java:46)
Caused by: ERROR XJ001: Java exception: '-1: java.lang.ArrayIndexOutOfBoundsException'.
        at org.apache.derby.iapi.error.StandardException.newException(Unknown Source)
        at org.apache.derby.impl.jdbc.SQLExceptionFactory.wrapArgsForTransportAcrossDRDA(Unknown Source)
        ... 12 more
Caused by: java.lang.ArrayIndexOutOfBoundsException: -1
        at org.apache.derby.impl.services.bytecode.BCMethod.popStack(Unknown Source)
        at org.apache.derby.impl.services.bytecode.BCMethod.callMethod(Unknown Source)
        at org.apache.derby.impl.sql.compile.ResultColumnList.generateEvaluatedRow(Unknown Source)
        at org.apache.derby.impl.sql.compile.MatchingClauseNode.generateInsertUpdateRow(Unknown Source)
        at org.apache.derby.impl.sql.compile.MatchingClauseNode.generate(Unknown Source)
        at org.apache.derby.impl.sql.compile.MergeNode.generate(Unknown Source)
        at org.apache.derby.impl.sql.compile.StatementNode.generate(Unknown Source)
        at org.apache.derby.impl.sql.GenericStatement.prepMinion(Unknown Source)
        at org.apache.derby.impl.sql.GenericStatement.prepare(Unknown Source)
        at org.apache.derby.impl.sql.conn.GenericLanguageConnectionContext.prepareInternalStatement(Unknown Source)
        ... 4 more