title: ExtJS infinite loop on grid focus
body: <p>We're using ExtJS 4.2 and ran into weird problem.
  There's a grouped grid panel from which we drag elements to a tree panel. In most cases everything is working fine, but sometimes for unknown reason wrong item is dragged or it doesn't happen at all. In these cases call stack that's printed in console shows infinite loop:</p>
  
  <pre><code>Ext.dom.Query.Ext.core.DomQuery.Ext.DomQuery.DQ.filter
  Ext.dom.Query.Ext.core.DomQuery.Ext.DomQuery.DQ.is
  Ext.define.is
  Ext.define.getNode
  Ext.define.indexOf
  Ext.define.onLastFocusChanged
  Ext.define.setLastFocused
  Ext.define.focusRow
  Ext.define.onRowFocusExt.define.onLastFocusChanged
  Ext.define.setLastFocused
  Ext.define.focusRow
  Ext.define.onRowFocus
  ....
  Ext.define.onLastFocusChanged
  Ext.define.setLastFocused
  Ext.define.focusRow
  Ext.define.onRowFocus
  ....
  </code></pre>
  
  <p>Any attempts to deliberatelly replicate the bug had failed, and logging all information on grid events to console doesn't show anything unusual.</p>
  
  <p>Has anybody had this problem, and maybe fixed it successfully?</p>
  
  <p>Thanks</p>