diff --git a/src/kiri/client.js b/src/kiri/client.js
index a40d2feb..138edd9b 100644
--- a/src/kiri/client.js
+++ b/src/kiri/client.js
@@ -164,7 +164,7 @@ const client = exports({
     },
 
     // widget sync
-    sync(widgets) {
+    sync(widgets, copy) {
         if (!widgets) {
             widgets = kiri.api.widgets.all();
         }
@@ -180,7 +180,7 @@ const client = exports({
                     meta: widget.meta,
                     group: widget.group.id,
                     track: widget.track,
-                    vertices: vertices,
+                    vertices: copy ? vertices.slice() : vertices,
                     position: widget.mesh.position,
                 }, done => {
                     widget.modified = false;
diff --git a/src/kiri/function.js b/src/kiri/function.js
index 79ab0fa6..bc2fb94d 100644
--- a/src/kiri/function.js
+++ b/src/kiri/function.js
@@ -115,7 +115,7 @@ function prepareSlices(callback, scale = 1, offset = 0) {
         // force re-sync in belt mode
         client.clear();
     }
-    client.sync();
+    client.sync(undefined, isBelt);
     client.rotate(settings);
 
     function sliceNext() {