I have a panel with a bottom toolbar. when I open my page, sometimes this toolbar is being hidden, as like:

toolbar.png

and when I refresh it appears ok!!

Code:
{                    
xtype: 'panel',
region: 'center',
split: true,
frame: false, 
 id: 'Panel_1',
 animCollapse: false,
 frameHeader: false,
 dockedItems: [  
      {     
           xtype: 'toolbar',   
           dock: 'bottom',   
           frame: false,            
           id: 'BottomTB',       
           items: [
can't figur out what's wrong