Index: src/vdbe.c
==================================================================
--- src/vdbe.c
+++ src/vdbe.c
@@ -1025,10 +1025,15 @@
     assert( memIsValid(pIn1) );
     memAboutToChange(p, pOut);
     zMalloc = pOut->zMalloc;
     pOut->zMalloc = 0;
     sqlite3VdbeMemMove(pOut, pIn1);
+#ifdef SQLITE_DEBUG
+    if( pOut->pScopyFrom>=&aMem[p1] && pOut->pScopyFrom<&aMem[p1+pOp->p3] ){
+      pOut->pScopyFrom += p1 - pOp->p2;
+    }
+#endif
     pIn1->zMalloc = zMalloc;
     REGISTER_TRACE(p2++, pOut);
     pIn1++;
     pOut++;
   }

ADDED   test/tkt-d635236375.test
Index: test/tkt-d635236375.test
==================================================================
--- /dev/null
+++ test/tkt-d635236375.test
@@ -0,0 +1,38 @@
+# 2011 August 3
+#
+# The author disclaims copyright to this source code.  In place of
+# a legal notice, here is a blessing:
+#
+#    May you do good and not evil.
+#    May you find forgiveness for yourself and forgive others.
+#    May you share freely, never taking more than you give.
+#
+#***********************************************************************
+# This file implements regression tests for SQLite library.  The
+# focus of this file is testing that bug [d63523637517386191d634e]
+# has been fixed.
+#
+
+set testdir [file dirname $argv0]
+source $testdir/tester.tcl
+
+set ::testprefix tkt-d635236375
+
+do_test 1.0 {
+  execsql {
+    CREATE TABLE t1(id1 INTEGER PRIMARY KEY);
+    INSERT INTO t1 VALUES(9999);
+    CREATE TABLE t2(id2 INTEGER PRIMARY KEY);
+    INSERT INTO t2 VALUES(12345);
+    INSERT INTO t2 VALUES(54321);
+    SELECT DISTINCT id1 AS x, id1 AS y FROM t1, t2;
+  }
+} {9999 9999}
+do_test 1.1 {
+  execsql {
+    SELECT count(*) FROM t1, t2 GROUP BY id1, id1;
+  }
+} {2}
+
+
+finish_test