Index: src/where.c
==================================================================
--- src/where.c
+++ src/where.c
@@ -14,11 +14,11 @@
 ** generating the code that loops through a table looking for applicable
 ** rows.  Indices are selected and used to speed the search when doing
 ** so is applicable.  Because this module is responsible for selecting
 ** indices, you might also think of this module as the "query optimizer".
 **
-** $Id: where.c,v 1.302 2008/04/19 14:40:44 drh Exp $
+** $Id: where.c,v 1.303 2008/05/16 15:40:40 danielk1977 Exp $
 */
 #include "sqliteInt.h"
 
 /*
 ** The number of bits in a Bitmask.  "BMS" means "BitMask Size".
@@ -2353,10 +2353,11 @@
                                                   pBestIdx->aConstraintUsage;
       const struct sqlite3_index_constraint *aConstraint =
                                                   pBestIdx->aConstraint;
 
       iReg = sqlite3GetTempRange(pParse, nConstraint+2);
+      pParse->disableColCache++;
       for(j=1; j<=nConstraint; j++){
         int k;
         for(k=0; k<nConstraint; k++){
           if( aUsage[k].argvIndex==j ){
             int iTerm = aConstraint[k].iTermOffset;
@@ -2364,10 +2365,11 @@
             break;
           }
         }
         if( k==nConstraint ) break;
       }
+      pParse->disableColCache--;
       sqlite3VdbeAddOp2(v, OP_Integer, pBestIdx->idxNum, iReg);
       sqlite3VdbeAddOp2(v, OP_Integer, j-1, iReg+1);
       sqlite3VdbeAddOp4(v, OP_VFilter, iCur, brk, iReg, pBestIdx->idxStr,
                         pBestIdx->needToFreeIdxStr ? P4_MPRINTF : P4_STATIC);
       sqlite3ReleaseTempRange(pParse, iReg, nConstraint+2);

ADDED   test/tkt3121.test
Index: test/tkt3121.test
==================================================================
--- /dev/null
+++ test/tkt3121.test
@@ -0,0 +1,51 @@
+# 2008 May 16
+#
+# 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.
+#
+#***********************************************************************
+#
+# $Id: tkt3121.test,v 1.1 2008/05/16 15:40:40 danielk1977 Exp $
+
+set testdir [file dirname $argv0]
+source $testdir/tester.tcl
+
+ifcapable !vtab {
+  finish_test
+  return
+}
+
+# Register the module
+register_echo_module [sqlite3_connection_pointer db]
+
+do_test vtabD-1.1 {
+  execsql {
+    PRAGMA encoding = 'utf16';
+
+    CREATE TABLE r1(field);
+    CREATE TABLE r2(col PRIMARY KEY, descr);
+
+    INSERT INTO r1 VALUES('abcd');
+    INSERT INTO r2 VALUES('abcd', 'A nice description');
+    INSERT INTO r2 VALUES('efgh', 'Another description');
+
+    CREATE VIRTUAL TABLE t1 USING echo(r1);
+    CREATE VIRTUAL TABLE t2 USING echo(r2);
+  }
+} {}
+
+do_test vtabD-1.2 {
+  execsql {
+    select
+      t1.field as Field,
+      t2.descr as Descr
+    from t1 inner join t2 on t1.field = t2.col order by t1.field
+  }
+} {abcd {A nice description}}
+
+finish_test
+