Datagrid not scrolling completely incase of variable row height used with renderer as editor

I need help in flex datagrid bug. I have a MX datagrid which has renderer as editors and variable row height.
My renderers have textarea which shows up whenever they receive focus ,The problem is whenever user is at bottom rows and if renderers receive focus.The datagrid doesnt scroll completely and the rows get clipped.
Please find attached screen shot .
Please help me to get a possible solution for this.i also have attached a sample code to demonstrate the issue and recieve possible solutions.