I am encountering a problem similar to How can I make datagrid height is equal to data content in Adobe Flex however suggested answers did not work for me.
The blank row at the end of the DataGrid does not display at first, until I begin editing editing the last row, at which the entire grid is immediately pushed upwards, making the top row disappear and the blank bottom row reappear.
Nikhil's answer in that post said that setting the height to count the overall height including the header as well as setting the verticalScrollPolicy to off still did not help me.