Fix T76155: 'Object lost data' on copy-pasting with new undo code.

source/blender/blenloader/intern/readfile.c

@@ -9659,7 +9659,9 @@ static bool read_libblock_undo_restore(
     /* Do not add LIB_TAG_NEW here, this should not be needed/used in undo case anyway (as
      * this is only for do_version-like code), but for sake of consistency, and also because
      * it will tell us which ID is re-used from old Main, and which one is actually new. */
-    const int id_tag = tag | LIB_TAG_NEED_LINK | LIB_TAG_UNDO_OLD_ID_REUSED;
+    /* Also do not add LIB_TAG_NEED_LINK, those IDs will never be re-liblinked, hence that tag will
+     * never be cleared, leading to critical issue in link/appemd code. */
+    const int id_tag = tag | LIB_TAG_UNDO_OLD_ID_REUSED;
     read_libblock_undo_restore_identical(fd, main, id, id_old, id_tag);
 
     /* Insert into library map for lookup by newly read datablocks (with pointer value bhead->old).