diff --git a/src/app/command_driver/clipboard.rs b/src/app/command_driver/clipboard.rs
index 73baecd4d..383c69413 100644
--- a/src/app/command_driver/clipboard.rs
+++ b/src/app/command_driver/clipboard.rs
@@ -578,6 +578,8 @@ pub(crate) fn paste_entities_kernel(
     // A pasted associative hatch follows the pasted boundary, or drops the
     // association when the boundary was not pasted with it. (#1370)
     crate::scene::remap_hatch_associations(doc, &handle_map);
+    // Reactors on the source drawing's objects do not travel with the paste.
+    crate::scene::remap_copied_reactors(doc, &handle_map);
     let leader_links: Vec<(Handle, Handle)> = entities
         .iter()
         .filter_map(|source| {
diff --git a/src/app/update/file.rs b/src/app/update/file.rs
index f671242bd..d5618c9dd 100644
--- a/src/app/update/file.rs
+++ b/src/app/update/file.rs
@@ -1883,6 +1883,11 @@ impl OpenCADStudio {
         // A file saved without the built-in Standard styles (foreign
         // or damaged) gets them re-seeded so nothing dangles (#366).
         crate::app::style_ops::ensure_standard_styles(&mut self.tabs[i].scene.document);
+        // Copies made by earlier releases kept their source's dimension
+        // association; such a file is reported as damaged elsewhere.
+        crate::scene::dimension_assoc::drop_stray_dimension_reactors(
+            &mut self.tabs[i].scene.document,
+        );
         // Follow the file's saved current UCS from the moment it opens.
         self.tabs[i].adopt_active_ucs_from_header();
         // Adopt the drawing's own Ortho ($ORTHOMODE) and running OSNAP
diff --git a/src/scene/dimension_assoc.rs b/src/scene/dimension_assoc.rs
index cf469b6b2..0498fb713 100644
--- a/src/scene/dimension_assoc.rs
+++ b/src/scene/dimension_assoc.rs
@@ -2434,3 +2434,50 @@ fn persisted_measurement_scale(
         viewport_compensation: calculated,
     })
 }
+
+/// Drop reactors an entity holds on a dimension association it has no part
+/// in: neither the association's dimension nor geometry it references. Copies
+/// made by earlier releases kept their source's association this way, which
+/// the reference application reports as a damaged drawing. Returns how many
+/// reactors were dropped.
+pub(crate) fn drop_stray_dimension_reactors(document: &mut codec::CadDocument) -> usize {
+    let associations: rustc_hash::FxHashMap<Handle, (Handle, Vec<Handle>)> = document
+        .objects
+        .iter()
+        .filter_map(|(handle, object)| {
+            let ObjectType::Associative(object) = object else {
+                return None;
+            };
+            let AssociativeData::DimensionAssociation(association) = &object.data else {
+                return None;
+            };
+            let geometry = association
+                .references
+                .iter()
+                .flatten()
+                .flat_map(|reference| {
+                    reference.xrefs.iter().chain(&reference.intersection_objects).copied()
+                })
+                .collect();
+            Some((*handle, (association.dimension, geometry)))
+        })
+        .collect();
+    if associations.is_empty() {
+        return 0;
+    }
+    let mut dropped = 0;
+    let handles: Vec<Handle> = document.entities().map(|entity| entity.common().handle).collect();
+    for handle in handles {
+        let Some(entity) = document.get_entity_mut(handle) else {
+            continue;
+        };
+        let reactors = &mut entity.common_mut().reactors;
+        let before = reactors.len();
+        reactors.retain(|reactor| match associations.get(reactor) {
+            Some((dimension, geometry)) => *dimension == handle || geometry.contains(&handle),
+            None => true,
+        });
+        dropped += before - reactors.len();
+    }
+    dropped
+}
diff --git a/src/scene/group_layer.rs b/src/scene/group_layer.rs
index 03c19ad92..71c857eee 100644
--- a/src/scene/group_layer.rs
+++ b/src/scene/group_layer.rs
@@ -114,6 +114,13 @@ impl Scene {
                 }
                 self.record_undo_object_before(gh, None);
             }
+            for member in group.entities.clone() {
+                if let Some(entity) = self.document.get_entity_mut(member) {
+                    if !entity.common().reactors.contains(&gh) {
+                        entity.common_mut().reactors.push(gh);
+                    }
+                }
+            }
             self.document.objects.insert(gh, ObjectType::Group(group));
             if let Some(ObjectType::Dictionary(dict)) =
                 self.document.objects.get_mut(&group_dict_handle)
diff --git a/src/scene/mod.rs b/src/scene/mod.rs
index 56f5be5c3..a2b7c264d 100644
--- a/src/scene/mod.rs
+++ b/src/scene/mod.rs
@@ -44,6 +44,7 @@ mod group_layer;
 mod layout;
 mod limits;
 mod modify;
+pub(crate) use modify::remap_copied_reactors;
 mod mspace;
 pub mod viewport_ref;
 pub mod viewport_dimension_pick;
diff --git a/src/scene/modify.rs b/src/scene/modify.rs
index 2ffb9bea6..ac069dcaf 100644
--- a/src/scene/modify.rs
+++ b/src/scene/modify.rs
@@ -823,6 +823,7 @@ impl Scene {
 
             let _ = self.sync_displayed_annotation_context(leader_handle);
         }
+        remap_copied_reactors(&mut self.document, &handle_map);
         // Complete group copies record their new Group objects and dictionary
         // entry as targeted object deltas inside copy_complete_groups.
         self.copy_complete_groups(&handle_map);
@@ -1803,3 +1804,20 @@ impl Scene {
         }
     }
 }
+
+/// A copy reacts only to what was copied with it: each reactor of the source
+/// that maps to a copy follows it there, and the rest (the source's dimension
+/// association, group, associative hatch) are dropped. The association and
+/// group copies add their own reactors afterwards.
+pub(crate) fn remap_copied_reactors(
+    document: &mut codec::CadDocument,
+    handle_map: &rustc_hash::FxHashMap<Handle, Handle>,
+) {
+    for &copy in handle_map.values() {
+        let Some(entity) = document.get_entity_mut(copy) else {
+            continue;
+        };
+        let reactors = &mut entity.common_mut().reactors;
+        *reactors = reactors.iter().filter_map(|reactor| handle_map.get(reactor).copied()).collect();
+    }
+}