In line 203 (in onDestroy) there is an if missing. Comparing the Ext JS 3.2.1 version of the RowExpander with yours I think the onDestroy function should look like this:

PHP Code:
if (this.keyNav) {
    
this.keyNav.disable();
    
delete this.keyNav;

var 
mainBody this.grid.getView().mainBody;
mainBody && mainBody.un'mousedown'this.onMouseDownthis);