diff --git a/internal/api/handler_config.go b/internal/api/handler_config.go
index 97157e494..19755f11c 100644
--- a/internal/api/handler_config.go
+++ b/internal/api/handler_config.go
@@ -485,6 +485,9 @@ func (h *Handler) updateServiceConfig(ctx context.Context, req *events.LambdaFun
 	// GET response carries them, so a client that echoes it back must not
 	// get them into the merged row; the store takes both from the database.
 	cfg.CreatedAt, cfg.UpdatedAt = nil, nil
+	// The plan-group fields (#1746) belong only to purchase plan entries; a
+	// global service setting never carries them, even on a first save.
+	cfg.GroupID, cfg.BoundIdentities, cfg.MaxStepCommitment = "", nil, nil
 
 	parts := strings.SplitN(service, "/", 2)
 	if len(parts) == 2 {
diff --git a/internal/api/handler_config_stamps_test.go b/internal/api/handler_config_stamps_test.go
index aff74bc86..a7b892a10 100644
--- a/internal/api/handler_config_stamps_test.go
+++ b/internal/api/handler_config_stamps_test.go
@@ -85,3 +85,38 @@ func TestUpdateServiceConfig_IgnoresClientStamps(t *testing.T) {
 	assert.Nil(t, saved.UpdatedAt, "a client-supplied updated_at must not reach the store")
 	assert.Equal(t, 80.0, saved.Coverage, "the editable fields still apply")
 }
+
+// TestUpdateServiceConfig_IgnoresClientGroupFields: the plan-group fields
+// (issue #1746) belong only to purchase plan entries, so a first save of a
+// global service setting must not store a client's group_id,
+// bound_identities or max_step_commitment.
+func TestUpdateServiceConfig_IgnoresClientGroupFields(t *testing.T) {
+	ctx := context.Background()
+	mockAuth := new(MockAuthService)
+	t.Cleanup(func() { mockAuth.AssertExpectations(t) })
+	mockAuth.On("ValidateSession", ctx, "admin-token").Return(&Session{
+		UserID: "aaaaaaaa-aaaa-aaaa-aaaa-aaaaaaaaaaaa", Email: "admin@example.com",
+	}, nil)
+	mockAuth.grantAdmin()
+
+	mockStore := new(MockConfigStore)
+	t.Cleanup(func() { mockStore.AssertExpectations(t) })
+	mockStore.On("GetServiceConfig", ctx, "aws", "rds").Return(nil, nil)
+	var saved *config.ServiceConfig
+	mockStore.On("SaveServiceConfig", ctx, mock.AnythingOfType("*config.ServiceConfig")).
+		Run(func(args mock.Arguments) { saved = args.Get(1).(*config.ServiceConfig) }).
+		Return(nil)
+	handler := &Handler{config: mockStore, auth: mockAuth}
+
+	_, err := handler.updateServiceConfig(ctx, &events.LambdaFunctionURLRequest{
+		Headers: map[string]string{"Authorization": "Bearer admin-token"},
+		Body: `{"enabled": true, "term": 3, "payment": "all-upfront", "coverage": 80,
+			"group_id": "g1", "bound_identities": ["k1"], "max_step_commitment": 50}`,
+	}, "aws/rds")
+	require.NoError(t, err)
+	require.NotNil(t, saved)
+	assert.Empty(t, saved.GroupID)
+	assert.Nil(t, saved.BoundIdentities)
+	assert.Nil(t, saved.MaxStepCommitment)
+	assert.Equal(t, 80.0, saved.Coverage, "the editable fields still apply")
+}
diff --git a/internal/api/handler_plans.go b/internal/api/handler_plans.go
index 236c94f1d..9434fe58e 100644
--- a/internal/api/handler_plans.go
+++ b/internal/api/handler_plans.go
@@ -472,6 +472,11 @@ func mergeUpdatedPlan(existingPlan *config.PurchasePlan, req *PlanRequest, planI
 func preserveRampProgress(existingPlan, plan *config.PurchasePlan) error {
 	plan.LastExecutionDate = existingPlan.LastExecutionDate
 	plan.LastNotificationSent = existingPlan.LastNotificationSent
+	// A bound plan keeps its marker across any ramp edit: without it the plan
+	// would buy by filter instead of its selected recommendations (#1746).
+	if existingPlan.RampSchedule.AllocationMode == config.RampAllocationBoundGroups {
+		plan.RampSchedule.AllocationMode = config.RampAllocationBoundGroups
+	}
 
 	if rampScheduleShapeUnchanged(existingPlan.RampSchedule, plan.RampSchedule) {
 		plan.RampSchedule.Type = existingPlan.RampSchedule.Type
diff --git a/internal/api/handler_plans_bound_marker_test.go b/internal/api/handler_plans_bound_marker_test.go
new file mode 100644
index 000000000..e65c0c5d5
--- /dev/null
+++ b/internal/api/handler_plans_bound_marker_test.go
@@ -0,0 +1,39 @@
+package api
+
+import (
+	"testing"
+
+	"github.com/LeanerCloud/cloud-commitments-platform/internal/config"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+// Fixtures are hand-built plans, not real configuration (issue #1746).
+
+// A PUT before step 1 may change the ramp shape, but a bound plan must keep
+// its bound_groups marker: dropping it would let the plan buy by filter.
+func TestUpdatePlan_KeepsBoundGroupsMarker(t *testing.T) {
+	const planID = "12345678-1234-1234-1234-123456789abc"
+	weekly := config.PresetRampSchedules[config.RampWeekly25Pct]
+	for _, tc := range []struct {
+		name, body string
+		stored     config.RampAllocationMode
+		want       config.RampAllocationMode
+	}{
+		{"shape change keeps bound_groups", `{"name":"p","ramp_schedule":"monthly-10pct"}`, config.RampAllocationBoundGroups, config.RampAllocationBoundGroups},
+		// (guard) the same shape already carried every mode.
+		{"same shape keeps bound_groups", `{"name":"renamed","ramp_schedule":"weekly-25pct"}`, config.RampAllocationBoundGroups, config.RampAllocationBoundGroups},
+		// (guard) other modes still reset on a shape change, as today.
+		{"shape change still drops equal_count", `{"name":"p","ramp_schedule":"monthly-10pct"}`, config.RampAllocationEqualCount, ""},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			rs := weekly
+			rs.AllocationMode = tc.stored
+			existing := &config.PurchasePlan{ID: planID, Name: "p", Enabled: true, RampSchedule: rs}
+			resp, saved := putPlan(t, existing, tc.body)
+			require.Equal(t, 200, resp.StatusCode, resp.Body)
+			require.NotNil(t, saved)
+			assert.Equal(t, tc.want, saved.RampSchedule.AllocationMode)
+		})
+	}
+}