Jvm will crash when the uncommitted characters exceeds the visible length of a JTextField.
To reproduce it, open jdk\demo\jfc\Metalworks, click "File-New", in the subject text field, switch to Chinese input method, type 'a' repeatly, jvm will crash when the ccharacters exceeds the visible length of a JTextField. It might reproduce with Japanese input method , too.
It reproduces with Mustang and 5.0, and might be reproducible with 1.4.