There seems to be an issue simulating the backspace key with java.awt.Robot.
This thread seems to confirm this but it does not propose a solution.
The Backspace functionality does not work as expected. I added a Shift key with the Backspace and it works fine for me, here is the pseudo-code for it.
robot.keyPress(KeyEvent.VK_SHIFT);
robot.keyPress(KeyEvent.VK_BACK_SPACE);
robot.keyRelease(KeyEvent.VK_BACK_SPACE);
robot.keyRelease(KeyEvent.VK_SHIFT);
This does not seem to work for the Delete key though.