Index: src/vdbesort.c
==================================================================
--- src/vdbesort.c
+++ src/vdbesort.c
@@ -885,34 +885,28 @@
 ** Free all resources owned by the object indicated by argument pTask. All 
 ** fields of *pTask are zeroed before returning.
 */
 static void vdbeSortSubtaskCleanup(sqlite3 *db, SortSubtask *pTask){
   sqlite3DbFree(db, pTask->pUnpacked);
-  pTask->pUnpacked = 0;
 #if SQLITE_MAX_WORKER_THREADS>0
   /* pTask->list.aMemory can only be non-zero if it was handed memory
   ** from the main thread.  That only occurs SQLITE_MAX_WORKER_THREADS>0 */
   if( pTask->list.aMemory ){
     sqlite3_free(pTask->list.aMemory);
-    pTask->list.aMemory = 0;
   }else
 #endif
   {
     assert( pTask->list.aMemory==0 );
     vdbeSorterRecordFree(0, pTask->list.pList);
   }
-  pTask->list.pList = 0;
   if( pTask->file.pFd ){
     sqlite3OsCloseFree(pTask->file.pFd);
-    pTask->file.pFd = 0;
-    pTask->file.iEof = 0;
   }
   if( pTask->file2.pFd ){
     sqlite3OsCloseFree(pTask->file2.pFd);
-    pTask->file2.pFd = 0;
-    pTask->file2.iEof = 0;
   }
+  memset(pTask, 0, sizeof(SortSubtask));
 }
 
 #ifdef SQLITE_DEBUG_SORTER_THREADS
 static void vdbeSorterWorkDebug(SortSubtask *pTask, const char *zEvent){
   i64 t;
@@ -1088,10 +1082,11 @@
   vdbeMergeEngineFree(pSorter->pMerger);
   pSorter->pMerger = 0;
   for(i=0; i<pSorter->nTask; i++){
     SortSubtask *pTask = &pSorter->aTask[i];
     vdbeSortSubtaskCleanup(db, pTask);
+    pTask->pSorter = pSorter;
   }
   if( pSorter->list.aMemory==0 ){
     vdbeSorterRecordFree(0, pSorter->list.pList);
   }
   pSorter->list.pList = 0;

Index: test/orderby1.test
==================================================================
--- test/orderby1.test
+++ test/orderby1.test
@@ -493,7 +493,36 @@
   CREATE INDEX t7ab ON t7(a,b);
   EXPLAIN QUERY PLAN
   SELECT * FROM t7 WHERE a=?1 ORDER BY rowid;
 } {~/ORDER BY/}
 
+#-------------------------------------------------------------------------
+# Test a partial sort large enough to cause the sorter to spill data
+# to disk.
+#
+reset_db
+do_execsql_test 8.0 {
+  PRAGMA cache_size = 5;
+  CREATE TABLE t1(a, b);
+  CREATE INDEX i1 ON t1(a);
+}
+
+do_eqp_test 8.1 {
+  SELECT * FROM t1 ORDER BY a, b;
+} {
+  0 0 0 {SCAN TABLE t1 USING INDEX i1} 
+  0 0 0 {USE TEMP B-TREE FOR RIGHT PART OF ORDER BY}
+}
+
+do_execsql_test 8.2 {
+  WITH cnt(i) AS (
+    SELECT 1 UNION ALL SELECT i+1 FROM cnt WHERE i<10000
+  )
+  INSERT INTO t1 SELECT i%2, randomblob(500) FROM cnt;
+}
+
+do_test 8.3 {
+  db eval { SELECT * FROM t1 ORDER BY a, b } { incr res $a }
+  set res
+} 5000
 
 finish_test