diff --git a/go/delivery/judge.go b/go/delivery/judge.go
index f030401..1aef5da 100644
--- a/go/delivery/judge.go
+++ b/go/delivery/judge.go
@@ -3,6 +3,7 @@ package delivery
 import (
 	"bytes"
 	"encoding/json"
+	"fmt"
 	"path"
 	"sort"
 	"strings"
@@ -84,9 +85,6 @@ func judged(from, to Composed) (Judgement, string) {
 	if ids := changedOf(before, after, func(kind string) bool { return kind == string(declaration.TypeContainer) }); len(ids) > 0 {
 		return JudgedRecreates, "it recreates " + strings.Join(ids, ", ")
 	}
-	if from.Data != to.Data {
-		return JudgedMovesData, "its data declaration changes"
-	}
 	places := dataPlaces(before, after)
 	held := func(kind string) bool {
 		return kind == string(declaration.TypeDirectory) || kind == string(declaration.TypeFile)
@@ -104,9 +102,20 @@ func judged(from, to Composed) (Judgement, string) {
 	if to.Data || from.Data {
 		moved = append(moved, changedOf(before, after, func(kind string) bool { return kind == string(declaration.TypeProcess) })...)
 	}
+	// A data flag that differs is no move of data by itself: data moves only when a data item does (issue 1126, 2026-10-29:
+	// a running composition read back from the kept declaration carries no flag, and mongodb's toolchain move asked a yes for
+	// moving its data). It is said loudly in the words, and never hides an item that moved.
 	if len(moved) > 0 {
 		sort.Strings(moved)
-		return JudgedMovesData, "it changes where its data is kept: " + strings.Join(moved, ", ")
+		words := "it changes where its data is kept: " + strings.Join(moved, ", ")
+		if from.Data != to.Data {
+			words += fmt.Sprintf("; its data flag differs too (running %v, composed %v)", from.Data, to.Data)
+		}
+		return JudgedMovesData, words
+	}
+	if from.Data != to.Data {
+		return JudgedNeither, fmt.Sprintf("it recreates no container and moves no data; WARNING: its data flag differs "+
+			"(running %v, composed %v) while no data item does, so one side's flag is wrong", from.Data, to.Data)
 	}
 	return JudgedNeither, "it recreates no container and moves no data"
 }
diff --git a/go/delivery/judge_test.go b/go/delivery/judge_test.go
index 4e61fd5..2ffa7c1 100644
--- a/go/delivery/judge_test.go
+++ b/go/delivery/judge_test.go
@@ -48,7 +48,8 @@ func TestJudgeMove(t *testing.T) {
 		{"a container gone", mail('a', true, container, spool), mail('b', true, spool), JudgedRecreates, false},
 		{"its spool moved", mail('a', true, container, spool), mail('b', true, container, spoolMoved), JudgedMovesData, false},
 		{"a file in its spool", mail('a', true, container, spool, config), mail('b', true, container, spool, config2), JudgedMovesData, false},
-		{"its data declaration", mail('a', false, container, spool), mail('b', true, container, spool), JudgedMovesData, false},
+		{"its data flag alone", mail('a', false, container, spool), mail('b', true, container, spool), JudgedNeither, false},
+		{"its data flag and its spool", mail('a', false, container, spool), mail('b', true, container, spoolMoved), JudgedMovesData, false},
 		{"a process of a module with data", mail('a', true, spool, process), mail('b', true, spool, process2), JudgedMovesData, false},
 		{"a process of a module without", mail('a', false, process), mail('b', false, process2), JudgedNeither, false},
 		{"its tools only", mail('a', true, container, spool, tools), mail('b', true, container, spool, tools2), JudgedNeither, false},
@@ -61,6 +62,9 @@ func TestJudgeMove(t *testing.T) {
 		if got.Judgement != c.want || got.UserListOnly != c.userList || got.Words == "" {
 			t.Errorf("%s: %+v, want %s (user list only %v)", c.name, got, c.want, c.userList)
 		}
+		if strings.Contains(c.name, "data flag alone") && !strings.Contains(got.Words, "WARNING: its data flag differs") {
+			t.Errorf("%s: the flag's difference is not said: %q", c.name, got.Words)
+		}
 	}
 	if got := JudgeMove(nil, Composed{Node: "ace"}); got.Judgement != JudgedNeither {
 		t.Errorf("the node's own composition: %+v", got)