Customer reported intermittent problems on certain hardware.

The following scenario was reported to occur several times
per day on Windows Vista:

a JFrame window is getting popped up as a dialog window. It contains
one JTextField, one JPasswordField, one JLabel element, and two
JButton elements, and is used as a 'logon' user dialog.
Intermittently character input into the textfields is no longer
echoed. The textfields just stay blank.
The application apparently hangs.

Moving an external window over the dialog window, and subsequently
removing it, triggers the redraw of the whole dialog window and
restores the expected contents. At that point in time the application
has resumed working as expected.