diff --git a/src/app/block_editor_tests.rs b/src/app/block_editor_tests.rs
index 48d452a52..26bdd79a8 100644
--- a/src/app/block_editor_tests.rs
+++ b/src/app/block_editor_tests.rs
@@ -54,6 +54,46 @@ fn main_depth(app: &OpenCADStudio) -> usize {
         .unwrap_or(tab.history.undo_stack.len())
 }
 
+#[test]
+fn local_undo_preserves_imported_native_networks_when_constraints_are_unchanged() {
+    use codec::objects::{AssocNetwork, AssociativeData, AssociativeObject, Dictionary, ObjectType};
+    let (mut app, reference) = fixture();
+    let i = app.active_tab;
+    let doc = &mut app.tabs[i].scene.document;
+    let owner = doc.block_records.get("EDIT_ME").unwrap().handle;
+    let dictionary_handle = doc.allocate_handle();
+    let network_handle = doc.allocate_handle();
+    let mut dictionary = Dictionary::new();
+    dictionary.handle = dictionary_handle;
+    dictionary.owner = owner;
+    dictionary.hard_owner = true;
+    dictionary.add_entry("ACAD_ASSOCNETWORK", network_handle);
+    doc.objects
+        .insert(dictionary_handle, ObjectType::Dictionary(dictionary));
+    let network = AssociativeObject {
+        handle: network_handle,
+        owner: dictionary_handle,
+        reactors: vec![dictionary_handle],
+        dxf_name: "ASSOCNETWORK".into(),
+        cpp_class_name: "AcDbAssocNetwork".into(),
+        data: AssociativeData::Network(AssocNetwork::default()),
+        ..Default::default()
+    };
+    doc.objects
+        .insert(network_handle, ObjectType::Associative(network));
+    begin(&mut app, reference);
+    let original_objects = app.tabs[i].scene.document.objects.clone();
+    circle(&mut app, 1.0);
+    assert!(!app.save_block_edit_as(i, "COPY"));
+    assert_eq!(app.tabs[i].scene.document.objects, original_objects);
+    app.undo_steps(1);
+    assert_eq!(members(&app).len(), 1);
+    assert_eq!(app.tabs[i].scene.document.objects, original_objects);
+    app.redo_steps(1);
+    assert_eq!(members(&app).len(), 2);
+    assert_eq!(app.tabs[i].scene.document.objects, original_objects);
+}
+
 #[test]
 fn save_as_forks_unsaved_edits_and_undoes_as_one_drawing_step() {
     let (mut app, reference) = fixture();
diff --git a/src/app/history.rs b/src/app/history.rs
index 04b2fb37f..649135591 100644
--- a/src/app/history.rs
+++ b/src/app/history.rs
@@ -1126,6 +1126,7 @@ impl OpenCADStudio {
         i: usize,
         had_full: bool,
         layer_panel_changed: bool,
+        native_graph_changed: bool,
         changes: &[(Handle, crate::scene::ChangeKind)],
     ) {
         self.tabs[i].edit_revision = self.tabs[i].edit_revision.wrapping_add(1);
@@ -1173,7 +1174,11 @@ impl OpenCADStudio {
                     }
                 }
             }
-            scene.sync_native_parametric_graph();
+            // Geometry or visibility replay does not change the constraint
+            // model. Rebuilding its graph would replace imported networks.
+            if native_graph_changed {
+                scene.sync_native_parametric_graph();
+            }
             scene.clear_preview_wire();
         }
         // UCS state is cached separately from its persisted header/viewport
@@ -1216,6 +1221,7 @@ impl OpenCADStudio {
         let mut last_label = String::new();
         let mut had_full = false;
         let mut layer_panel_changed = false;
+        let mut native_graph_changed = false;
         let mut changes = Vec::new();
         for _ in 0..steps {
             let Some(snapshot) = self.tabs[i].history.undo_stack.pop() else {
@@ -1225,6 +1231,8 @@ impl OpenCADStudio {
             let step_label = last_label.clone();
             match snapshot {
                 HistorySnapshot::Delta(mut d) => {
+                    native_graph_changed |=
+                        !d.parametric_constraints.is_empty() || d.named_parameters.is_some();
                     // Symmetric: undo applies the before side, then the same
                     // delta rides to the redo stack (it still holds the after
                     // side) — no current-state capture needed.
@@ -1259,7 +1267,13 @@ impl OpenCADStudio {
             }
             self.refedit_after_history_step(i, &step_label, true);
         }
-        self.finish_history_apply(i, had_full, layer_panel_changed, &changes);
+        self.finish_history_apply(
+            i,
+            had_full,
+            layer_panel_changed,
+            native_graph_changed,
+            &changes,
+        );
         self.command_line
             .push_output(crate::tf!("Undo: {last_label}").as_ref());
     }
@@ -1278,6 +1292,7 @@ impl OpenCADStudio {
         let mut last_label = String::new();
         let mut had_full = false;
         let mut layer_panel_changed = false;
+        let mut native_graph_changed = false;
         let mut changes = Vec::new();
         for _ in 0..steps {
             let Some(snapshot) = self.tabs[i].history.redo_stack.pop() else {
@@ -1287,6 +1302,8 @@ impl OpenCADStudio {
             let step_label = last_label.clone();
             match snapshot {
                 HistorySnapshot::Delta(mut d) => {
+                    native_graph_changed |=
+                        !d.parametric_constraints.is_empty() || d.named_parameters.is_some();
                     layer_panel_changed |= d.structure.as_ref().is_some_and(|structure| {
                         matches!(
                             structure,
@@ -1318,7 +1335,13 @@ impl OpenCADStudio {
             }
             self.refedit_after_history_step(i, &step_label, false);
         }
-        self.finish_history_apply(i, had_full, layer_panel_changed, &changes);
+        self.finish_history_apply(
+            i,
+            had_full,
+            layer_panel_changed,
+            native_graph_changed,
+            &changes,
+        );
         self.command_line
             .push_output(crate::tf!("Redo: {last_label}").as_ref());
     }