Merge pull request #3484 from Autodesk/deboisj/EMSUSD-796_reenable_su…

…btree_fallback_on_notif

EMSUSD-796 Send subtree invalidate on undo mark instanceable.

lib/usdUfe/ufe/StagesSubject.cpp

@@ -467,19 +467,17 @@ void StagesSubject::stageChanged(
                         sentNotif = true;
                         break;
                     }
-                    // Note : Do nothing here with didRemoveInertPrim and didRemoveNonInertPrim.
-                    // Indeed, we can get these if prim specs are removed from some layers, but it
-                    // does not mean that the prim is no longer in the composed stage. If the prim
-                    // was actually gone, we would either get an invalid prim (in which case we
-                    // would not even get here, and would send a object destroyed" notif in the else
-                    // below), or we would fall into the "HasInfoChange : Active" case below. If
-                    // nothing else sends a notif in the loop (typically via the info change :
-                    // active) we do not want to send the fallback notif, so act as if a notif was
-                    // sent.
-                    else if (
-                        entry->flags.didRemoveInertPrim || entry->flags.didRemoveNonInertPrim) {
-                        sentNotif = true;
-                    }
+                    // Note : Do not send ObjectDelete notifs when didRemoveInertPrim or
+                    // didRemoveNonInertPrim are set. Indeed, we can get these if prim
+                    // specs are removed from some layers, but it does not mean that the prim is no
+                    // longer in the composed stage. If the prim was actually gone, we would either
+                    // get an invalid prim (in which case we would not even get here, and would send
+                    // a object destroyed" notif in the else below), or we would fall into the
+                    // "HasInfoChange : Active" case below. However, let the fallback
+                    // SubtreeInvalidate notif be sent, as it is sometimes required (for example
+                    // when unmarking a prim as instanceable - we get entries with the inert prim
+                    // removed, as its instanced version is removed, but it is still there as a
+                    // regular prim and needs to be invalidated.
 
                     // Special case for "active" metadata.
                     if (entry->HasInfoChange(SdfFieldKeys->Active)) {