diff --git a/apps/common/main/lib/component/Mixtbar.js b/apps/common/main/lib/component/Mixtbar.js
index 2547d2a61e..77a666a377 100644
--- a/apps/common/main/lib/component/Mixtbar.js
+++ b/apps/common/main/lib/component/Mixtbar.js
@@ -745,7 +745,7 @@ define([
                     _maxright = box_controls_width;
                 if (!_staticPanelWidth) _staticPanelWidth = 0;
                 var _rightedge = $active.outerWidth() + _staticPanelWidth,
-                    delta = (this._prevBoxWidth) ? (_maxright - this._prevBoxWidth) : -1,
+                    delta = (this._prevBoxWidth!==undefined) ? (_maxright - this._prevBoxWidth) : -1,
                     hideAllMenus = false;
                 this._prevBoxWidth = _maxright;
                 more_section.is(':visible') && (_maxright -= more_section_width);