Cursor can become invisible in text area when the following steps are done:
 * click on button (sets text to null)
 * click into TextArea
 * click on button again
 * click into TextArea again
 * cursor is notvisible, changing focus does not help but typing into TextArea does

I can see this behavior since 8u20, 8u5 and 8u11 throws NPE while setting null value (probably RT-34959), 7u75 works.